Linux/Documentation/io-mapping.txt

Chinese translated version of Linux/Documentation/io-mapping.txt

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Linux/Documentation/io-mapping.txt的中文翻译




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The io_mapping functions in linux/io-mapping.h provide an abstraction forefficiently mapping small regions of an I/O device to the CPU. The initialusage is to support the large graphics aperture on 32-bit processors whereioremap_wc cannot be used to statically map the entire aperture to the CPUas it would consume too much of the kernel address space.s

在linux/io-mappin文件里io-mapping函数提供了个抽象为有效映射到cpu的io设备的小区域。

最初的用法是支持32位机器上ioremapwc不能静态映射的cpu的孔而导致消耗大量的内核地址。

A mapping object is created during driver initialization using  一个映射对象是在驱动初始化的时候被创建的。       struct io_mapping *io_mapping_create_wc(unsigned long base,                                               unsigned long size)                'base' is the bus address of the region to be made               mappable, while 'size' indicates how large a mapping region to               enable. Both are in bytes.  base参数表示可映射的区域总线地址，size参数表示映射区域的有效范围。                This _wc variant provides a mapping which may only be used                with the io_mapping_map_atomic_wc or io_mapping_map_wc.

wc变量提供一个只能被io_mapping_map_atomic_wc 或者 io_mapping_map_wc使用的映射。

  With this mapping object, individual pages can be mapped either atomically  or not, depending on the necessary scheduling environment. Of course, atomic  maps are more efficient:  有了这个映射对象，根据所需的环境，个别页能够原子级别的映射。原子映射更加高效。          void *io_mapping_map_atomic_wc(struct io_mapping *mapping,                                         unsigned long offset)   'offset' is the offset within the defined mapping region.  Accessing addresses beyond the region specified in the  creation function yields undefined results. Using an offset  which is not page aligned yields an undefined result. The  return value points to a single page in CPU address space. offest参数表示所定义的映射区域的偏移，在指定的区域范围内访问地址  创建函数产生不确定的结果，使用的偏移量 。 这是不是页对齐产生未定义的结果。返回值指向cpu地址空间的一个单页。

  This _wc variant returns a write-combining map to the  page and may only be used with mappings created by  io_mapping_create_wc wc变量返回一个到页的写结合映射，也可能被io_mapping_create_wc所创造的映射使用  Note that the task may not sleep while holding this page  mapped.   void io_mapping_unmap_atomic(void *vaddr)   'vaddr' must be the the value returned by the last   io_mapping_map_atomic_wc call. This unmaps the specified   page and allows the task to sleep once again. vaddr必须是io_mapping_map_atomic_wc做后一次调用返回的结果。这取消映射指定   页面，并且允许任务再次入睡。  If you need to sleep while holding the lock, you can use the non-atomic  variant, although they may be significantly slower.  如果你在加锁的时候睡眠， 你需要使用non-atomic变量，尽管这可能导致变慢。        void *io_mapping_map_wc(struct io_mapping *mapping,                                unsigned long offset)    This works like io_mapping_map_atomic_wc except it allows    the task to sleep while holding the page mapped.    像io-mapping-map-atomic-wc一样的工作期待它允许任务在拥有页映射时睡眠      void io_mapping_unmap(void *vaddr)      This works like io_mapping_unmap_atomic, except it is used     for pages mapped with io_mapping_map_wc.     像io-mapping-map-atomic-wc一样的工作期待被页映射使用     At driver close time, the io_mapping object must be freed:         void io_mapping_free(struct io_mapping *mapping)   Current Implementation:   The initial implementation of these functions uses existing mapping  mechanisms and so provides only an abstraction layer and no new  functionality.  这些函数的初始接口使用存在的映射机制，提供一个没有新功能的抽象层。 On 64-bit processors, io_mapping_create_wc calls ioremap_wc for the whole range, creating a permanent kernel-visible mapping to the resource. The map_atomic and map functions add the requested offset to the base of the virtual address returned by ioremap_wc. 在64位处理器，io_mapping_create_wc调用ioremap_wc的整个范围，建立一个永久性的内核可见映射到资源。kmap_atomic的映射功能添 加所需的偏移的虚拟地址的基础上由ioremap_wc返回。  On 32-bit processors with HIGHMEM defined, io_mapping_map_atomic_wc uses  kmap_atomic_pfn to map the specified page in an atomic fashion;  kmap_atomic_pfn isn't really supposed to be used with device pages, but it  provides an efficient mapping for this usage.  在32位处理器与HIGHMEM定义，io_mapping_map_atomic_wc使用kmap_atomic的PFN以原子方式映射到指定的页面; kmap_atomic_pfn不  是真的应该用于与设备的网页，但它提供了一个高效的映射。  On 32-bit processors without HIGHMEM defined, io_mapping_map_atomic_wc and  io_mapping_map_wc both use ioremap_wc, a terribly inefficient function which  performs an IPI to inform all processors about the new mapping. This results  i在32位处理器没有HIGHMEM定义，io_mapping_map_atomic_wc  io_mapping_map_wc使用ioremap_wc，一个非常低效的功能  进行IPI告知所有处理器的新的映射。这样导致  一个显着的性能损失。