[PATCH] usb: ehci: Fix "EHCI timed out on TD - token=XXXX" error on ehci-hcd

Tom Rini trini at konsulko.com
Mon Mar 2 20:54:28 CET 2020

On Mon, Mar 02, 2020 at 08:19:22PM +0100, Marek Vasut wrote:
> On 3/2/20 2:21 PM, Lukasz Majewski wrote:
> > Hi,
> Hi,
> >> This patch aims to improve robustness of 'usb' command operation on
> >> the ehci-hcd IP block as it ports to contemporary U-Boot the patch
> >> described and provided in [1] (originally applicable to U-Boot
> >> 2016.05).
> >>
> >> According to the fix author - "rayvt" (from [1]):
> >>
> >> TD stands for "Queue Element Transfer Descriptor (qTD)", which is a
> >> micro-code instruction for the EHCI USB chip.
> >> The "token" field is detailed information, control, and status of the
> >> TD's data transfer. In particular, the rightmost byte is the status
> >> field. 0x80 bit means the TD is active and the data transfer has not
> >> yet completed. 0x08 bit means there was some sort of data transfer
> >> error (XactErr).
> > 	 ^^^^^^^ - this error is NOT handled now in mainline u-boot. Do
> > 	 you have any experience with it?
> No, but then I also didn't run into those yet.
> >> If the drive gets a transfer error, it refuses to do any other I/O
> >> transfer until the error is properly cleared and reset. U-boot did
> >> not do this, so every subsequent disk read would get a timeout error
> >> because the drive would not send any data. The fix is to properly
> >> clear and reset the USB disk when it gets a transfer error.
> So basically, what this says is, "we crashed the drive, because the
> drive suffered counter overflow, thus we fix it by resetting the drive".
> No, the fix is to not crash the drive in the first place.
> >> Every read operation starts at the maximum block size. When the USB
> >> pendrive is not able to correctly serve this data read request, the
> >> dynamic reduction of IO size is performed. Up to six tries (with
> >> smaller IO block each time) are attempted.
> >>
> >> A related problem is that some drives are slow to come up. Linux
> >> handles this by issuing a spinup command and allowing more time for
> >> the drive to respond. The same idea is applied in this fix.
> >>
> >> On TPC70 (i.MX6Q) once per ~10 times (without this patch):
> >>
> >> Bus usb at 2184200: USB EHCI 1.00
> >> scanning bus usb at 2184200 for devices... 2 USB Device(s) found
> >>        scanning usb for storage devices... 1 Storage Device(s) found
> >> EHCI timed out on TD - token=0x1f8c80
> > 
> > This is how the error gets evident. The detailed explanation is in link
> > [1].
> Is there one specific post in that forum, or do I need to read through
> the whole multi-page thread ?
> I would expect that if you run -- I assume 'usb reset' (the command is
> missing above) -- then the bus gets power-cycled, hence the USB device
> also gets power-cycled.

FWIW, the problem I have does not get fixed via "usb reset".  Ethernet
never shows up again.  I do see right now that I disabled network tests
on the platform a long while ago for unknown reasons, but did comment to
myself elsewhere that network was fairly flaky in U-Boot.

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