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

[Guenter Roeck]

On Thu, Feb 27, 2020 at 02:06:55PM -0800, Doug Anderson wrote:
> 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.
> 
Added:

Fixes: 151d0cbdbe860 ("usb: dwc2: make the scheduler handle excessive NAKs better")

> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Thanks!

Guenter