usb

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HCD : usb host controller devices

uhci(universal host controller interface): Intel用在自家芯片组上的usb 1.1主控制器(host controller)的硬件实例
ehci(enhanced host controller interface): usb 2.0的主控制器标准接口。
ohci(open host controller inferface)：一个不仅仅是usb用的主控制器接口标准。主要是遵循csr (configuration space register)标准。是其他厂商在设计usb host controller时遵循的标准，如via, nec, ali, 包括nvidia等等。

不同的接口对应不同的桥接器

首先,EHCI和UHCI的区别之一就在于探寻她们内心世界的方式不同.甭管EHCI还是UHCI,她们都有自己的内心世界.访问外设的内心世界通常有两种方法,一种是Memory-mapped I/O,一种是Port-mapped I/O.EHCI和OHCI都是这种Memory-mapped I/O,而UHCI则剑走偏锋,选择了Port-mapped I/O.

int usb_hcd_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)中的一段代码

****

    if (driver->flags & HCD_MEMORY) {
       /* EHCI, OHCI */
       hcd->rsrc_start = pci_resource_start(dev, 0);
       hcd->rsrc_len = pci_resource_len(dev, 0);
       if (!request_mem_region(hcd->rsrc_start, hcd->rsrc_len,
               driver->description)) {
           dev_dbg(&dev->dev, "controller already in use\n");
           retval = -EBUSY;
           goto clear_companion;
       }
       hcd->regs = ioremap_nocache(hcd->rsrc_start, hcd->rsrc_len);
       if (hcd->regs == NULL) {
           dev_dbg(&dev->dev, "error mapping memory\n");
           retval = -EFAULT;
           goto release_mem_region;
       }

   } else {
       /* UHCI */
       int   region;

       for (region = 0; region < PCI_ROM_RESOURCE; region++) {
           if (!(pci_resource_flags(dev, region) &
                   IORESOURCE_IO))
               continue;

           hcd->rsrc_start = pci_resource_start(dev, region);
           hcd->rsrc_len = pci_resource_len(dev, region);
           if (request_region(hcd->rsrc_start, hcd->rsrc_len,
                   driver->description))
               break;
       }
       if (region == PCI_ROM_RESOURCE) {
           dev_dbg(&dev->dev, "no i/o regions available\n");
           retval = -EBUSY;
           goto clear_companion;
       }
   }

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