Re: [RFT PATCH 3/4] usb: dwc2: Abort transaction after errors with unknown reason

[Doug Anderson]

Hi,

On Wed, Feb 26, 2020 at 1:04 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> In some situations, the following error messages are reported.
>
> dwc2 ff540000.usb: dwc2_hc_chhltd_intr_dma: Channel 1 - ChHltd set, but reason is unknown
> dwc2 ff540000.usb: hcint 0x00000002, intsts 0x04000021
>
> This is sometimes followed by:
>
> dwc2 ff540000.usb: dwc2_update_urb_state_abn(): trimming xfer length
>
> and then:
>
> WARNING: CPU: 0 PID: 0 at kernel/v4.19/drivers/usb/dwc2/hcd.c:2913
>                         dwc2_assign_and_init_hc+0x98c/0x990
>
> The warning suggests that an odd buffer address is to be used for DMA.
>
> After an error is observed, the receive buffer may be full
> (urb->actual_length >= urb->length). However, the urb is still left in
> the queue unless three errors were observed in a row. When it is queued
> again, the dwc2 hcd code translates this into a 1-block transfer.
> If urb->actual_length (ie the total expected receive length) is not
> DMA-aligned, the buffer pointer programmed into the chip will be
> unaligned. This results in the observed warning.
>
> To solve the problem, abort input transactions after an error with
> unknown cause if the entire packet was already received. This may be
> a bit drastic, but we don't really know why the transfer was aborted
> even though the entire packet was received. Aborting the transfer in
> this situation is less risky than accepting a potentially corrupted
> packet.
>
> With this patch in place, the 'ChHltd set' and 'trimming xfer length'
> messages are still observed, but there are no more transfer attempts
> with odd buffer addresses.
>
> Cc: Boris ARZUR <boris@xxxxxxxxx>
> Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>  drivers/usb/dwc2/hcd_intr.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

Seems sane to me.  Also suggest a "Fixes" or "Cc: stable" tag.

Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>