Framebuffer驱动程序框架 skeletonfb.c 分析

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Framebuffer驱动程序框架 skeletonfb.c 分析

最近想好好研究一下lcd驱动开发过程，lcd驱动开发主要就是framebuffer的编写了，这里只要想做framebuffer驱动的开发可能这里是必经之路，因为这里这个skeletnfb.c是framebuffer驱动程序开发的骨架，他没有具体去实现任何功能，没有针对任何设备，但是，他的作用却十分惊人，他就是使用说明文档一样，教你怎样一步一步进行framebuffer驱动编写

写贴出这个架构的实现过程，下面再慢慢分析：

这里就开始慢慢啃一啃这个硬骨架吧

/*
 * linux/drivers/video/skeletonfb.c -- Skeleton for a frame buffer device
 *
 * Modified to new api Jan 2001 by James Simmons (jsimmons@transvirtual.com)
 *
 * Created 28 Dec 1997 by Geert Uytterhoeven
 *
 *
 * I have started rewriting this driver as a example of the upcoming new API
 * The primary goal is to remove the console code from fbdev and place it
 * into fbcon.c. This reduces the code and makes writing a new fbdev driver
 * easy since the author doesn't need to worry about console internals. It
 * also allows the ability to run fbdev without a console/tty system on top 
 * of it. 
 *
 * First the roles of struct fb_info and struct display have changed. Struct
 * display will go away. The way the new framebuffer console code will
 * work is that it will act to translate data about the tty/console in 
 * struct vc_data to data in a device independent way in struct fb_info. Then
 * various functions in struct fb_ops will be called to store the device 
 * dependent state in the par field in struct fb_info and to change the 
 * hardware to that state. This allows a very clean separation of the fbdev
 * layer from the console layer. It also allows one to use fbdev on its own
 * which is a bounus for embedded devices. The reason this approach works is 
 * for each framebuffer device when used as a tty/console device is allocated
 * a set of virtual terminals to it. Only one virtual terminal can be active 
 * per framebuffer device. We already have all the data we need in struct 
 * vc_data so why store a bunch of colormaps and other fbdev specific data
 * per virtual terminal. 
 *
 * As you can see doing this makes the con parameter pretty much useless
 * for struct fb_ops functions, as it should be. Also having struct 
 * fb_var_screeninfo and other data in fb_info pretty much eliminates the 
 * need for get_fix and get_var. Once all drivers use the fix, var, and cmap
 * fbcon can be written around these fields. This will also eliminate the
 * need to regenerate struct fb_var_screeninfo, struct fb_fix_screeninfo
 * struct fb_cmap every time get_var, get_fix, get_cmap functions are called
 * as many drivers do now. 
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License. See the file COPYING in the main directory of this archive for
 * more details.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/fb.h>
#include <linux/init.h>
#include <linux/pci.h>

/*
 * This is just simple sample code.
 * No warranty that it actually compiles.
 * Even less warranty that it actually works :-)
 */

/*
 * Driver data
 */
static char *mode_option __devinitdata;

/*
 * If your driver supports multiple boards, you should make the 
 * below data types arrays, or allocate them dynamically (using kmalloc()). 
 */ 

/* 
 * This structure defines the hardware state of the graphics card. Normally
 * you place this in a header file in linux/include/video. This file usually
 * also includes register information. That allows other driver subsystems
 * and userland applications the ability to use the same header file to 
 * avoid duplicate work and easy porting of software. 
 */
struct xxx_par;

/*
 * Here we define the default structs fb_fix_screeninfo and fb_var_screeninfo
 * if we don't use modedb. If we do use modedb see xxxfb_init how to use it
 * to get a fb_var_screeninfo. Otherwise define a default var as well. 
 */
static struct fb_fix_screeninfo xxxfb_fix __devinitdata = {
    .id =        "FB's name", 
    .type =        FB_TYPE_PACKED_PIXELS,
    .visual =    FB_VISUAL_PSEUDOCOLOR,
    .xpanstep =    1,
    .ypanstep =    1,
    .ywrapstep = 1, 
    .accel =    FB_ACCEL_NONE,
};

/*
 * Modern graphical hardware not only supports pipelines but some 
 * also support multiple monitors where each display can have its 
 * its own unique data. In this case each display could be 
 * represented by a separate framebuffer device thus a separate 
 * struct fb_info. Now the struct xxx_par represents the graphics
 * hardware state thus only one exist per card. In this case the 
 * struct xxx_par for each graphics card would be shared between 
 * every struct fb_info that represents a framebuffer on that card. 
 * This allows when one display changes it video resolution (info->var) 
 * the other displays know instantly. Each display can always be
 * aware of the entire hardware state that affects it because they share
 * the same xxx_par struct. The other side of the coin is multiple
 * graphics cards that pass data around until it is finally displayed
 * on one monitor. Such examples are the voodoo 1 cards and high end
 * NUMA graphics servers. For this case we have a bunch of pars, each
 * one that represents a graphics state, that belong to one struct 
 * fb_info. Their you would want to have *par point to a array of device
 * states and have each struct fb_ops function deal with all those 
 * states. I hope this covers every possible hardware design. If not
 * feel free to send your ideas at jsimmons@users.sf.net 
 */

/*
 * If your driver supports multiple boards or it supports multiple 
 * framebuffers, you should make these arrays, or allocate them 
 * dynamically using framebuffer_alloc() and free them with
 * framebuffer_release().
 */ 
static struct fb_info info;

/* 
 * Each one represents the state of the hardware. Most hardware have
 * just one hardware state. These here represent the default state(s). 
 */
static struct xxx_par __initdata current_par;

int xxxfb_init(void);

/**
 *    xxxfb_open - Optional function. Called when the framebuffer is first accessed.
 *    @info: frame buffer structure that represents a single frame buffer
 *    @user: tell us if the userland (value=1) or the console is accessing the framebuffer. 
 *
 *    This function is the first function called in the framebuffer api.
 *    Usually you don't need to provide this function. The case where it 
 *    is used is to change from a text mode hardware state to a graphics
 *     mode state. 
 *
 *    Returns negative errno on error, or zero on success.
 */
static int xxxfb_open(struct fb_info *info, int user)
{
    return 0;
}

/**
 *    xxxfb_release - Optional function. Called when the framebuffer device is closed. 
 *    @info: frame buffer structure that represents a single frame buffer
 *    @user: tell us if the userland (value=1) or the console is accessing the framebuffer. 
 *    
 *    Thus function is called when we close /dev/fb or the framebuffer 
 *    console system is released. Usually you don't need this function.
 *    The case where it is usually used is to go from a graphics state
 *    to a text mode state.
 *
 *    Returns negative errno on error, or zero on success.
 */
static int xxxfb_release(struct fb_info *info, int user)
{
    return 0;
}

/**
 * xxxfb_check_var - Optional function. Validates a var passed in. 
 * @var: frame buffer variable screen structure
 * @info: frame buffer structure that represents a single frame buffer 
 *    检查我们传入的var是否是硬件支持的属性，这个方法不改变硬件，也就是fb_info中保存的data不会改变
      这个方法用在我们只是想测试一下硬件，但并不是真正设置硬件属性
 *    Checks to see if the hardware supports the state requested by
 *    var passed in. This function does not alter the hardware 
 *    This means the data stored in struct fb_info and struct xxx_par do 
 *    not change. This includes the var inside of struct fb_info. 
 *    Do NOT change these. This function can be called on its own if we
 *    intent to only test a mode and not actually set it. The stuff in 
 *    modedb.c is a example of this. If the var passed in is slightly 
 *    off by what the hardware can support then we alter the var PASSED in
 *    to what we can do.
 *
 * For values that are off, this function must round them _up_ to the
 * next value that is supported by the hardware. If the value is
 * greater than the highest value supported by the hardware, then this
 * function must return -EINVAL.
 *
 * Exception to the above rule: Some drivers have a fixed mode, ie,
 * the hardware is already set at boot up, and cannot be changed. In
 * this case, it is more acceptable that this function just return
 * a copy of the currently working var (info->var). Better is to not
 * implement this function, as the upper layer will do the copying
 * of the current var for you.
 *
 * Note: This is the only function where the contents of var can be
 * freely adjusted after the driver has been registered. If you find
 * that you have code outside of this function that alters the content
 * of var, then you are doing something wrong. Note also that the
 * contents of info->var must be left untouched at all times after
 * driver registration.
 *
 *    Returns negative errno on error, or zero on success.
 */
static int xxxfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
{
    /* ... */
    return 0;         
}

/**
 * xxxfb_set_par - Optional function. Alters the hardware state.
 * @info: frame buffer structure that represents a single frame buffer
 *    使用这个方法是用来设置framebuffer属性的，会改变fb_info中的par和fb_fix_screeinfo数据，
      但是不改变var的数据
 *    Using the fb_var_screeninfo in fb_info we set the resolution of the
 *    this particular framebuffer. This function alters the par AND the
 *    fb_fix_screeninfo stored in fb_info. It doesn't not alter var in 
 *    fb_info since we are using that data. This means we depend on the
 *    data in var inside fb_info to be supported by the hardware. 
 *
 * This function is also used to recover/restore the hardware to a
 * known working state.
 *
 *    xxxfb_check_var is always called before xxxfb_set_par to ensure that
 * the contents of var is always valid.
 *
 *    Again if you can't change the resolution you don't need this function.
 *
 * However, even if your hardware does not support mode changing,
 * a set_par might be needed to at least initialize the hardware to
 * a known working state, especially if it came back from another
 * process that also modifies the same hardware, such as X.
 *
 * If this is the case, a combination such as the following should work:
 *
 * static int xxxfb_check_var(struct fb_var_screeninfo *var,
 * struct fb_info *info)
 * {
 * *var = info->var;
 * return 0;
 * }
 *
 * static int xxxfb_set_par(struct fb_info *info)
 * {
 * init your hardware here
 * }
 *
 *    Returns negative errno on error, or zero on success.
 */
static int xxxfb_set_par(struct fb_info *info)
{
    struct xxx_par *par = info->par;
    /* ... */
    return 0;    
}

/**
 *     xxxfb_setcolreg - Optional function. Sets a color register.
 * @regno: Which register in the CLUT we are programming 
 * @red: The red value which can be up to 16 bits wide 
 *    @green: The green value which can be up to 16 bits wide 
 *    @blue: The blue value which can be up to 16 bits wide.
 *    @transp: If supported, the alpha value which can be up to 16 bits wide.
 * @info: frame buffer info structure
 * 
 *     Set a single color register. The values supplied have a 16 bit
 *     magnitude which needs to be scaled in this function for the hardware. 
 *    Things to take into consideration are how many color registers, if
 *    any, are supported with the current color visual. With truecolor mode
 *    no color palettes are supported. Here a pseudo palette is created
 *    which we store the value in pseudo_palette in struct fb_info. For
 *    pseudocolor mode we have a limited color palette. To deal with this
 *    we can program what color is displayed for a particular pixel value.
 *    DirectColor is similar in that we can program each color field. If
 *    we have a static colormap we don't need to implement this function. 
 * 
 *    Returns negative errno on error, or zero on success.
 */
static int xxxfb_setcolreg(unsigned regno, unsigned red, unsigned green,
             unsigned blue, unsigned transp,
             struct fb_info *info)
{
    if (regno >= 256) /* no. of hw registers */
       return -EINVAL;
    /*
     * Program hardware... do anything you want with transp
     */

    /* grayscale works only partially under directcolor */
    if (info->var.grayscale) {
       /* grayscale = 0.30*R + 0.59*G + 0.11*B */
       red = green = blue = (red * 77 + green * 151 + blue * 28) >> 8;
    }

    /* Directcolor:
     * var->{color}.offset contains start of bitfield
     * var->{color}.length contains length of bitfield
     * {hardwarespecific} contains width of DAC
     * pseudo_palette[X] is programmed to (X << red.offset) |
     * (X << green.offset) |
     * (X << blue.offset)
     * RAMDAC[X] is programmed to (red, green, blue)
     * color depth = SUM(var->{color}.length)
     *
     *     Pseudocolor:
     * var->{color}.offset is 0 unless the palette index takes less than
     * bits_per_pixel bits and is stored in the upper
     * bits of the pixel value
     * var->{color}.length is set so that 1 << length is the number of
     * available palette entries
     * pseudo_palette is not used
     * RAMDAC[X] is programmed to (red, green, blue)
     * color depth = var->{color}.length
     *
     *     Static pseudocolor:
     * same as Pseudocolor, but the RAMDAC is not programmed (read-only)
     *
     *     Mono01/Mono10:
     * Has only 2 values, black on white or white on black (fg on bg),
     * var->{color}.offset is 0
     * white = (1 << var->{color}.length) - 1, black = 0
     * pseudo_palette is not used
     * RAMDAC does not exist
     * color depth is always 2
     *
     *     Truecolor:
     * does not use RAMDAC (usually has 3 of them).
     * var->{color}.offset contains start of bitfield
     * var->{color}.length contains length of bitfield
     * pseudo_palette is programmed to (red << red.offset) |
     * (green << green.offset) |
     * (blue << blue.offset) |
     * (transp << transp.offset)
     * RAMDAC does not exist
     * color depth = SUM(var->{color}.length})
     *
     *     The color depth is used by fbcon for choosing the logo and also
     *     for color palette transformation if color depth < 4
     *
     *    As can be seen from the above, the field bits_per_pixel is _NOT_
     *    a criteria for describing the color visual.
     *
     *    A common mistake is assuming that bits_per_pixel <= 8 is pseudocolor,
     *    and higher than that, true/directcolor. This is incorrect, one needs
     *    to look at the fix->visual.
     *
     *     Another common mistake is using bits_per_pixel to calculate the color
     *     depth. The bits_per_pixel field does not directly translate to color
     *     depth. You have to compute for the color depth (using the color
     *     bitfields) and fix->visual as seen above.
     */

    /*
     *     This is the point where the color is converted to something that
     *     is acceptable by the hardware.
     */
#define CNVT_TOHW(val,width) ((((val)<<(width))+0x7FFF-(val))>>16)
    red = CNVT_TOHW(red, info->var.red.length);
    green = CNVT_TOHW(green, info->var.green.length);
    blue = CNVT_TOHW(blue, info->var.blue.length);
    transp = CNVT_TOHW(transp, info->var.transp.length);
#undef CNVT_TOHW
    /*
     * This is the point where the function feeds the color to the hardware
     * palette after converting the colors to something acceptable by
     * the hardware. Note, only FB_VISUAL_DIRECTCOLOR and
     * FB_VISUAL_PSEUDOCOLOR visuals need to write to the hardware palette.
     * If you have code that writes to the hardware CLUT, and it's not
     * any of the above visuals, then you are doing something wrong.
     */
    if (info->fix.visual == FB_VISUAL_DIRECTCOLOR ||
    info->fix.visual == FB_VISUAL_TRUECOLOR)
     write_{red|green|blue|transp}_to_clut();

    /*This is the point were you need to fill up the contents of
     * info->pseudo_palette. This structure is used _only_ by fbcon, thus
     * it only contains 16 entries to match the number of colors supported
     * by the console. The pseudo_palette is used only if the visual is
     * in directcolor or truecolor mode. With other visuals, the
     * pseudo_palette is not used. (This might change in the future.)
     *
     * The contents of the pseudo_palette is in raw pixel format. Ie, each
     * entry can be written directly to the framebuffer without any conversion.
     * The pseudo_palette is (void *). However, if using the generic
     * drawing functions (cfb_imageblit, cfb_fillrect), the pseudo_palette
     * must be casted to (u32 *) _regardless_ of the bits per pixel. If the
     * driver is using its own drawing functions, then it can use whatever
     * size it wants.
     */
    if (info->fix.visual == FB_VISUAL_TRUECOLOR ||
    info->fix.visual == FB_VISUAL_DIRECTCOLOR) {
     u32 v;

     if (regno >= 16)
         return -EINVAL;

     v = (red << info->var.red.offset) |
         (green << info->var.green.offset) |
         (blue << info->var.blue.offset) |
         (transp << info->var.transp.offset);

     ((u32*)(info->pseudo_palette))[regno] = v;
    }

    /* ... */
    return 0;
}

/**
 * xxxfb_pan_display - NOT a required function. Pans the display.
 * @var: frame buffer variable screen structure
 * @info: frame buffer structure that represents a single frame buffer
 *
 * Pan (or wrap, depending on the `vmode' field) the display using the
 * 'xoffset' and `yoffset' fields of the `var' structure.
 * If the values don't fit, return -EINVAL.
 *
 * Returns negative errno on error, or zero on success.
 */
static int xxxfb_pan_display(struct fb_var_screeninfo *var,
             struct fb_info *info)
{
    /*
     * If your hardware does not support panning, _do_ _not_ implement this
     * function. Creating a dummy function will just confuse user apps.
     */

    /*
     * Note that even if this function is fully functional, a setting of
     * 0 in both xpanstep and ypanstep means that this function will never
     * get called.
     */

    /* ... */
    return 0;
}

/**
 * xxxfb_blank - NOT a required function. Blanks the display.
 * @blank_mode: the blank mode we want. 
 * @info: frame buffer structure that represents a single frame buffer
 *
 * Blank the screen if blank_mode != FB_BLANK_UNBLANK, else unblank.
 * Return 0 if blanking succeeded, != 0 if un-/blanking failed due to
 * e.g. a video mode which doesn't support it.
 *
 * Implements VESA suspend and powerdown modes on hardware that supports
 * disabling hsync/vsync:
 *
 * FB_BLANK_NORMAL = display is blanked, syncs are on.
 * FB_BLANK_HSYNC_SUSPEND = hsync off
 * FB_BLANK_VSYNC_SUSPEND = vsync off
 * FB_BLANK_POWERDOWN = hsync and vsync off
 *
 * If implementing this function, at least support FB_BLANK_UNBLANK.
 * Return !0 for any modes that are unimplemented.
 *
 */
static int xxxfb_blank(int blank_mode, struct fb_info *info)
{
    /* ... */
    return 0;
}

/* ------------ Accelerated Functions --------------------- */

/*
 * We provide our own functions if we have hardware acceleration
 * or non packed pixel format layouts. If we have no hardware 
 * acceleration, we can use a generic unaccelerated function. If using
 * a pack pixel format just use the functions in cfb_*.c. Each file 
 * has one of the three different accel functions we support.
 */

/**
 * xxxfb_fillrect - REQUIRED function. Can use generic routines if 
 *              non acclerated hardware and packed pixel based.
 *             Draws a rectangle on the screen.        
 *
 * @info: frame buffer structure that represents a single frame buffer
 *    @region: The structure representing the rectangular region we 
 *         wish to draw to.
 *
 *    This drawing operation places/removes a retangle on the screen 
 *    depending on the rastering operation with the value of color which
 *    is in the current color depth format.
 */
void xxxfb_fillrect(struct fb_info *p, const struct fb_fillrect *region)
{
/*    Meaning of struct fb_fillrect
 *
 *    @dx: The x and y corrdinates of the upper left hand corner of the 
 *    @dy: area we want to draw to. 
 *    @width: How wide the rectangle is we want to draw.
 *    @height: How tall the rectangle is we want to draw.
 *    @color:    The color to fill in the rectangle with. 
 *    @rop: The raster operation. We can draw the rectangle with a COPY
 *     of XOR which provides erasing effect. 
 */
}

/**
 * xxxfb_copyarea - REQUIRED function. Can use generic routines if
 * non acclerated hardware and packed pixel based.
 * Copies one area of the screen to another area.
 *
 * @info: frame buffer structure that represents a single frame buffer
 * @area: Structure providing the data to copy the framebuffer contents
 *     from one region to another.
 *
 * This drawing operation copies a rectangular area from one area of the
 *    screen to another area.
 */
void xxxfb_copyarea(struct fb_info *p, const struct fb_copyarea *area) 
{
/*
 * @dx: The x and y coordinates of the upper left hand corner of the
 *    @dy: destination area on the screen.
 * @width: How wide the rectangle is we want to copy.
 * @height: How tall the rectangle is we want to copy.
 * @sx: The x and y coordinates of the upper left hand corner of the
 * @sy: source area on the screen.
 */
}


/**
 * xxxfb_imageblit - REQUIRED function. Can use generic routines if
 * non acclerated hardware and packed pixel based.
 * Copies a image from system memory to the screen. 
 *
 * @info: frame buffer structure that represents a single frame buffer
 *    @image:    structure defining the image.
 *
 * This drawing operation draws a image on the screen. It can be a 
 *    mono image (needed for font handling) or a color image (needed for
 *    tux). 
 */
void xxxfb_imageblit(struct fb_info *p, const struct fb_image *image) 
{
/*
 * @dx: The x and y coordinates of the upper left hand corner of the
 *    @dy: destination area to place the image on the screen.
 * @width: How wide the image is we want to copy.
 * @height: How tall the image is we want to copy.
 * @fg_color: For mono bitmap images this is color data for 
 * @bg_color: the foreground and background of the image to
 *         write directly to the frmaebuffer.
 *    @depth:    How many bits represent a single pixel for this image.
 *    @data: The actual data used to construct the image on the display.
 *    @cmap: The colormap used for color images. 
 */

/*
 * The generic function, cfb_imageblit, expects that the bitmap scanlines are
 * padded to the next byte. Most hardware accelerators may require padding to
 * the next u16 or the next u32. If that is the case, the driver can specify
 * this by setting info->pixmap.scan_align = 2 or 4. See a more
 * comprehensive description of the pixmap below.
 */
}

/**
 *    xxxfb_cursor -     OPTIONAL. If your hardware lacks support
 *            for a cursor, leave this field NULL.
 *
 * @info: frame buffer structure that represents a single frame buffer
 *    @cursor: structure defining the cursor to draw.
 *
 * This operation is used to set or alter the properities of the cursor.
 *
 *    Returns negative errno on error, or zero on success.
 */
int xxxfb_cursor(struct fb_info *info, struct fb_cursor *cursor)
{
/*
 * @set:     Which fields we are altering in struct fb_cursor 
 *    @enable: Disable or enable the cursor 
 * @rop:     The bit operation we want to do. 
 * @mask: This is the cursor mask bitmap. 
 * @dest: A image of the area we are going to display the cursor.
 *        Used internally by the driver.     
 * @hot:    The hot spot. 
 *    @image:    The actual data for the cursor image.
 *
 * NOTES ON FLAGS (cursor->set):
 *
 * FB_CUR_SETIMAGE - the cursor image has changed (cursor->image.data)
 * FB_CUR_SETPOS - the cursor position has changed (cursor->image.dx|dy)
 * FB_CUR_SETHOT - the cursor hot spot has changed (cursor->hot.dx|dy)
 * FB_CUR_SETCMAP - the cursor colors has changed (cursor->fg_color|bg_color)
 * FB_CUR_SETSHAPE - the cursor bitmask has changed (cursor->mask)
 * FB_CUR_SETSIZE - the cursor size has changed (cursor->width|height)
 * FB_CUR_SETALL - everything has changed
 *
 * NOTES ON ROPs (cursor->rop, Raster Operation)
 *
 * ROP_XOR - cursor->image.data XOR cursor->mask
 * ROP_COPY - curosr->image.data AND cursor->mask
 *
 * OTHER NOTES:
 *
 * - fbcon only supports a 2-color cursor (cursor->image.depth = 1)
 * - The fb_cursor structure, @cursor, _will_ always contain valid
 * fields, whether any particular bitfields in cursor->set is set
 * or not.
 */
}

/**
 *    xxxfb_rotate - NOT a required function. If your hardware
 *            supports rotation the whole screen then 
 *            you would provide a hook for this. 
 *
 * @info: frame buffer structure that represents a single frame buffer
 *    @angle: The angle we rotate the screen. 
 *
 * This operation is used to set or alter the properities of the
 *    cursor.
 */
void xxxfb_rotate(struct fb_info *info, int angle)
{
/* Will be deprecated */
}

/**
 *    xxxfb_sync - NOT a required function. Normally the accel engine 
 *         for a graphics card take a specific amount of time.
 *         Often we have to wait for the accelerator to finish
 *         its operation before we can write to the framebuffer
 *         so we can have consistent display output. 
 *
 * @info: frame buffer structure that represents a single frame buffer
 *
 * If the driver has implemented its own hardware-based drawing function,
 * implementing this function is highly recommended.
 */
int xxxfb_sync(struct fb_info *info)
{
    return 0;
}

    /*
     * Frame buffer operations
     */

static struct fb_ops xxxfb_ops = {
    .owner        = THIS_MODULE,
    .fb_open    = xxxfb_open,
    .fb_read    = xxxfb_read,
    .fb_write    = xxxfb_write,
    .fb_release    = xxxfb_release,
    .fb_check_var    = xxxfb_check_var,
    .fb_set_par    = xxxfb_set_par,
    .fb_setcolreg    = xxxfb_setcolreg,
    .fb_blank    = xxxfb_blank,
    .fb_pan_display    = xxxfb_pan_display,
    .fb_fillrect    = xxxfb_fillrect,     /* Needed !!! */
    .fb_copyarea    = xxxfb_copyarea,    /* Needed !!! */
    .fb_imageblit    = xxxfb_imageblit,    /* Needed !!! */
    .fb_cursor    = xxxfb_cursor,        /* Optional !!! */
    .fb_rotate    = xxxfb_rotate,
    .fb_sync    = xxxfb_sync,
    .fb_ioctl    = xxxfb_ioctl,
    .fb_mmap    = xxxfb_mmap,
};

/* ------------------------------------------------------------------------- */

/*
 * Initialization
 */
这里他们的定义是不一样的，唯一的不同
/* static int __init xxfb_probe (struct platform_device *pdev) -- for platform devs */
static int __devinit xxxfb_probe(struct pci_dev *dev, const struct pci_device_id *ent)
{
    struct fb_info *info;
    struct xxx_par *par;
    struct device *device = &dev->dev; /* or &pdev->dev */
    int cmap_len, retval;    
   
    /*
     * Dynamically allocate info and par
     */
    info = framebuffer_alloc(sizeof(struct xxx_par), device);

    if (!info) {
     /* goto error path */
    }

    par = info->par;把我们驱动中的私有数据指向info->par，我们在上面已经通过framebuffer_alloc为他申请了内存

    /* 
     * Here we set the screen_base to the virtual memory address
     * for the framebuffer. Usually we obtain the resource address
     * from the bus layer and then translate it to virtual memory
     * space via ioremap. Consult ioport.h. 
     */
    这里注释也已经说的很清楚了，我们通常通过注册好的设备信息获取到memory address，然后把这个地址转换为virtual memory通过ioremap这个方法
    info->screen_base = framebuffer_virtual_memory;
    info->fbops = &xxxfb_ops;这个定义好的xxxfb_ops结构中包含了用户空间访问driver的所有方法，用户访问/dev/fb0最终通过fbmem中注册的方法调用这里的方法
    info->fix = xxxfb_fix; /* this will be the only time xxxfb_fix will be used, so mark it as __devinitdata */
    info->pseudo_palette = pseudo_palette; /* The pseudopalette is an 16-member array*/
    /*
     * Set up flags to indicate what sort of acceleration your
     * driver can provide (pan/wrap/copyarea/etc.) and whether it
     * is a module -- see FBINFO_* in include/linux/fb.h
     *
     * If your hardware can support any of the hardware accelerated functions
     * fbcon performance will improve if info->flags is set properly.
     *
     * FBINFO_HWACCEL_COPYAREA - hardware moves
     * FBINFO_HWACCEL_FILLRECT - hardware fills
     * FBINFO_HWACCEL_IMAGEBLIT - hardware mono->color expansion
     * FBINFO_HWACCEL_YPAN - hardware can pan display in y-axis
     * FBINFO_HWACCEL_YWRAP - hardware can wrap display in y-axis
     * FBINFO_HWACCEL_DISABLED - supports hardware accels, but disabled
     * FBINFO_READS_FAST - if set, prefer moves over mono->color expansion
     * FBINFO_MISC_TILEBLITTING - hardware can do tile blits
     *
     * NOTE: These are for fbcon use only.
     */
    info->flags = FBINFO_DEFAULT;

/********************* This stage is optional ******************************/
     /*
     * The struct pixmap is a scratch pad for the drawing functions. This
     * is where the monochrome bitmap is constructed by the higher layers
     * and then passed to the accelerator. For drivers that uses
     * cfb_imageblit, you can skip this part. For those that have a more
     * rigorous requirement, this stage is needed
     */

    /* PIXMAP_SIZE should be small enough to optimize drawing, but not
     * large enough that memory is wasted. A safe size is
     * (max_xres * max_font_height/8). max_xres is driver dependent,
     * max_font_height is 32.
     */
    info->pixmap.addr = kmalloc(PIXMAP_SIZE, GFP_KERNEL);
    if (!info->pixmap.addr) {
     /* goto error */
    }

    info->pixmap.size = PIXMAP_SIZE;

    /*
     * FB_PIXMAP_SYSTEM - memory is in system ram
     * FB_PIXMAP_IO - memory is iomapped
     * FB_PIXMAP_SYNC - if set, will call fb_sync() per access to pixmap,
     * usually if FB_PIXMAP_IO is set.
     *
     * Currently, FB_PIXMAP_IO is unimplemented.
     */
    info->pixmap.flags = FB_PIXMAP_SYSTEM;

    /*
     * scan_align is the number of padding for each scanline. It is in bytes.
     * Thus for accelerators that need padding to the next u32, put 4 here.
     */
    info->pixmap.scan_align = 4;

    /*
     * buf_align is the amount to be padded for the buffer. For example,
     * the i810fb needs a scan_align of 2 but expects it to be fed with
     * dwords, so a buf_align = 4 is required.
     */
    info->pixmap.buf_align = 4;

    /* access_align is how many bits can be accessed from the framebuffer
     * ie. some epson cards allow 16-bit access only. Most drivers will
     * be safe with u32 here.
     *
     * NOTE: This field is currently unused.
     */
    info->pixmap.access_align = 32;
/***************************** End optional stage ***************************/

    /*
     * This should give a reasonable default video mode. The following is
     * done when we can set a video mode. 
     */
    if (!mode_option)
    mode_option = "640x480@60";         

    retval = fb_find_mode(&info->var, info, mode_option, NULL, 0, NULL, 8);
  
    if (!retval || retval == 4)
    return -EINVAL;            

    /* This has to be */
    if (fb_alloc_cmap(&info->cmap, cmap_len, 0))
    return -ENOMEM;
    
    /* 
     * The following is done in the case of having hardware with a static 
     * mode. If we are setting the mode ourselves we don't call this. 
     */    
    info->var = xxxfb_var;

    /*
     * For drivers that can...
     */
    xxxfb_check_var(&info->var, info);

    /*
     * Does a call to fb_set_par() before register_framebuffer needed? This
     * will depend on you and the hardware. If you are sure that your driver
     * is the only device in the system, a call to fb_set_par() is safe.
     *
     * Hardware in x86 systems has a VGA core. Calling set_par() at this
     * point will corrupt the VGA console, so it might be safer to skip a
     * call to set_par here and just allow fbcon to do it for you.
     */
    /* xxxfb_set_par(info); */

    if (register_framebuffer(info) < 0) {注册设备，fbmem中负责注册了一个fb 字符设备，只有调用了这个方法，才真正创建了这个fb字符设备
    fb_dealloc_cmap(&info->cmap);
    return -EINVAL;
    }
    printk(KERN_INFO "fb%d: %s frame buffer device\n", info->node,
     info->fix.id);
    pci_set_drvdata(dev, info); /* or platform_set_drvdata(pdev, info) */方便后面使用info这个结构中的所有数据
    return 0;
}

    /*
     * Cleanup
     */
/* static void __devexit xxxfb_remove(struct platform_device *pdev) */
static void __devexit xxxfb_remove(struct pci_dev *dev)
{
    struct fb_info *info = pci_get_drvdata(dev);
    /* or platform_get_drvdata(pdev); */

    if (info) {
        unregister_framebuffer(info);
        fb_dealloc_cmap(&info->cmap);
        /* ... */
        framebuffer_release(info);
    }
}

#ifdef CONFIG_PCI
#ifdef CONFIG_PM
/**
 *    xxxfb_suspend - Optional but recommended function. Suspend the device.
 *    @dev: PCI device
 *    @msg: the suspend event code.
 *
 * See Documentation/power/devices.txt for more information
 */
static int xxxfb_suspend(struct pci_dev *dev, pm_message_t msg)
{
    struct fb_info *info = pci_get_drvdata(dev);
    struct xxxfb_par *par = info->par;

    /* suspend here */
    return 0;
}

/**
 *    xxxfb_resume - Optional but recommended function. Resume the device.
 *    @dev: PCI device
 *
 * See Documentation/power/devices.txt for more information
 */
static int xxxfb_resume(struct pci_dev *dev)
{
    struct fb_info *info = pci_get_drvdata(dev);
    struct xxxfb_par *par = info->par;

    /* resume here */
    return 0;
}
#else
#define xxxfb_suspend NULL
#define xxxfb_resume NULL
#endif /* CONFIG_PM */

static struct pci_device_id xxxfb_id_table[] = {
    { PCI_VENDOR_ID_XXX, PCI_DEVICE_ID_XXX,
     PCI_ANY_ID, PCI_ANY_ID, PCI_BASE_CLASS_DISPLAY << 16,
     PCI_CLASS_MASK, 0 },
    { 0, }
};

/* For PCI drivers */
static struct pci_driver xxxfb_driver = {
    .name =        "xxxfb",
    .id_table =    xxxfb_id_table,
    .probe =    xxxfb_probe,
    .remove =    __devexit_p(xxxfb_remove),
    .suspend = xxxfb_suspend, /* optional but recommended */
    .resume = xxxfb_resume, /* optional but recommended */
};

MODULE_DEVICE_TABLE(pci, xxxfb_id_table);

int __init xxxfb_init(void)
{
    /*
     * For kernel boot options (in 'video=xxxfb:<options>' format)
     */
#ifndef MODULE
    char *option = NULL;

    if (fb_get_options("xxxfb", &option))
        return -ENODEV;
    xxxfb_setup(option);
#endif

    return pci_register_driver(&xxxfb_driver);
}

static void __exit xxxfb_exit(void)
{
    pci_unregister_driver(&xxxfb_driver);
}
#else /* non PCI, platform drivers */
#include <linux/platform_device.h>
/* for platform devices */

#ifdef CONFIG_PM
/**
 *    xxxfb_suspend - Optional but recommended function. Suspend the device.
 *    @dev: platform device
 *    @msg: the suspend event code.
 *
 * See Documentation/power/devices.txt for more information
 */
static int xxxfb_suspend(struct platform_device *dev, pm_message_t msg)
{
    struct fb_info *info = platform_get_drvdata(dev);
    struct xxxfb_par *par = info->par;

    /* suspend here */
    return 0;
}

/**
 *    xxxfb_resume - Optional but recommended function. Resume the device.
 *    @dev: platform device
 *
 * See Documentation/power/devices.txt for more information
 */
static int xxxfb_resume(struct platform_dev *dev)
{
    struct fb_info *info = platform_get_drvdata(dev);
    struct xxxfb_par *par = info->par;

    /* resume here */
    return 0;
}
#else
#define xxxfb_suspend NULL
#define xxxfb_resume NULL
#endif /* CONFIG_PM */

static struct platform_device_driver xxxfb_driver = {
    .probe = xxxfb_probe,
    .remove = xxxfb_remove,
    .suspend = xxxfb_suspend, /* optional but recommended */
    .resume = xxxfb_resume, /* optional but recommended */
    .driver = {
        .name = "xxxfb",
    },
};

static struct platform_device *xxxfb_device;

#ifndef MODULE
    /*
     * Setup
     */

/*
 * Only necessary if your driver takes special options,
 * otherwise we fall back on the generic fb_setup().
 */
int __init xxxfb_setup(char *options)
{
    /* Parse user speficied options (`video=xxxfb:') */
}
#endif /* MODULE */

static int __init xxxfb_init(void)
{
    int ret;
    /*
     * For kernel boot options (in 'video=xxxfb:<options>' format)
     */
#ifndef MODULE
    char *option = NULL;

    if (fb_get_options("xxxfb", &option))
        return -ENODEV;
    xxxfb_setup(option);
#endif
    ret = platform_driver_register(&xxxfb_driver);

    if (!ret) {
        xxxfb_device = platform_device_register_simple("xxxfb", 0,
                                NULL, 0);

        if (IS_ERR(xxxfb_device)) {
            platform_driver_unregister(&xxxfb_driver);
            ret = PTR_ERR(xxxfb_device);
        }
    }

    return ret;
}

static void __exit xxxfb_exit(void)
{
    platform_device_unregister(xxxfb_device);
    platform_driver_unregister(&xxxfb_driver);
}
#endif /* CONFIG_PCI */

/* ------------------------------------------------------------------------- */


    /*
     * Modularization
     */

module_init(xxxfb_init);
module_exit(xxxfb_remove);

MODULE_LICENSE("GPL");

这里就开始慢慢啃一啃这个硬骨架吧

毫无疑问，先找到module_init(xxxfb_init)，xxxfb_init这个方式是这个驱动的入口，我们要找到这个方法，代码中我已经标注出来，原来在这个架构中采用了两种方法来实现framebuffer驱动，分别是pci子系统方式和platform子系统方式，这里他们的实现方法基本相似，只是在匹配device时有所不同，我们没有必要过于关注这里，大家也可以看到，他们的proble方法是一样的，这个proble才是我们要真正好好分析的

第一件事就是为fb_info动态申请内存空间，很有必要分析一下这个方法

/**
 * framebuffer_alloc - creates a new frame buffer info structure
 *
 * @size: size of driver private data, can be zero
 * @dev: pointer to the device for this fb, this can be NULL
 *
 * Creates a new frame buffer info structure. Also reserves @size bytes
 * for driver private data (info->par). info->par (if any) will be
 * aligned to sizeof(long).
 *
 * Returns the new structure, or NULL if an error occured.
 *
 */
struct fb_info *framebuffer_alloc(size_t size, struct device *dev)
{
#define BYTES_PER_LONG (BITS_PER_LONG/8)
#define PADDING (BYTES_PER_LONG - (sizeof(struct fb_info) % BYTES_PER_LONG))
    int fb_info_size = sizeof(struct fb_info);
    struct fb_info *info;
    char *p;

    if (size)
        fb_info_size += PADDING;

    p = kzalloc(fb_info_size + size, GFP_KERNEL);

    if (!p)
        return NULL;

    info = (struct fb_info *) p;

    if (size)
        info->par = p + fb_info_size;

    info->device = dev;

#ifdef CONFIG_FB_BACKLIGHT
    mutex_init(&info->bl_curve_mutex);
#endif

    return info;
#undef PADDING
#undef BYTES_PER_LONG
}

其实这里注释也已经说清楚了，这个方法不止为fb_info申请了内存空间，还为fb_info中的一个void型指针par分配了内存空间，这个par将会保存之后在这个驱动中的私有变量，是一个结构，保存了很多driver的相关信息，保存到par中，之后想要使用的时候就很容易得到
这个架构中的其他方法都没有实现，他们就是访问driver时候具体的处理函数，就是要我们要去花大力气去做的事情
之后在真正的framebuffer驱动程序中再去好好分析这些方法吧
待续。。。。。。