[U-Boot] [PATCH 1/1] tegra: usb: Fix device enumeration problem of USB1

[Jim Lin]

On 06/14/2012 04:40 AM, Jim Lin wrote:
>> For some reason, bit 1 (connect status change) of PORTSC will be set
>> after issuing Port Reset (like "usb reset" in u-boot command line).
>> This will be treated as an error and stops later device enumeration.
>> 
>> Therefore we add a definition in header file to ignore checking of that bit
>> after Port Reset.
>> CONFIG_USB_RESET_IGNORE_CONNECT_CHANGE

>(Again, I'm CC'ing the USB maintainer here)

>Looking at the Linux kernel's Tegra EHCI driver:
>a) This WAR is only needed on the first USB port, not all of them.

  [Jim] No penalty for USB2 and USB3 ports. Because u-boot hub_port_reset
  has at most 5 times of retry for a port.
  USB2 and USB3 ports will reset once in retry loop
  ('port connect change' bit will not set after reset).
  USB1 will have at most 2 times of reset in the retry loop after adding
  this patch.

>b) This WAR is not complete; there's a loop in the kernel that resets
>the port twice in order to guarantee that the port will become enabled.

  [Jim] Disagree. Because u-boot hub_port_reset has at most 5 times of retry
  for a port. U-boot and kernel code are not entirely same.

>c) The kernel driver actively clears this CSC bit rather than leaving it
>set and ignoring it. Is there any implication to this difference?

  [Jim] I can make next change to be consistent with kernel driver to clear
  CSC bit after Port Reset.

>So, rather than just ifdef'ing this fix into the driver, wouldn't it be
>better to add a callback from the USB core into the USB driver, so that
>the Tegra EHCI driver could choose to only implement this WAR for port
>1, and also do the multiple-reset-loop thing.

  [Jim] No callback for me to cut in. Also no penalty for other ports.

>Finally, in the change description, the text "for some reason" is quite
>unclear; it sounds like you have absolutely no idea why this happens. Is
>this a known and root-caused HW bug for which this fix has been fully
>validated? Or, is this patch just some random hack that seems to work
>for you?

  [Jim] This is a known and root-caused HW bug.
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