Re: [PATCH v2 1/1] usb: xhci: fix checking ep busy for CFC

[Mathias Nyman]

On 29.10.2015 14:58, Lu, Baolu wrote:
> On 10/29/2015 08:51 PM, Sergei Shtylyov wrote:
> > Hello.
> >
> > On 10/29/2015 5:46 AM, Lu Baolu wrote:
> >
> > > Function ep_ring_is_processing() checks the dequeue pointer
> > > in endpoint context to know whether an endpoint is busy with
> > > processing TRBs. This is not correct since dequeue pointer
> > > field in an endpoint context is only valid when the endpoint
> > > is in Halted or Stopped states. This buggy code causes audio
> > > noise when playing sound with USB headset connected to host
> > > controllers which support CFC (one of xhci 1.1 features).
> > >
> > > This patch should exist in stable kernel since v4.3.
> > >
> > > Reported-and-tested-by: YD Tseng <yd_tseng@xxxxxxxxxxxxxx>
> > > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > >
> > > ---
> > > v1->v2:
> > > Implement the logic in xhci_queue_isoc_tx_prepare() instead of
> > > a seperated function as suggested by Mathias.
> > >
> > > ---
> > >   drivers/usb/host/xhci-ring.c | 32 ++++++--------------------------
> > >   1 file changed, 6 insertions(+), 26 deletions(-)
> > >
> > > diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> > > index fa83625..8edc286 100644
> > > --- a/drivers/usb/host/xhci-ring.c
> > > +++ b/drivers/usb/host/xhci-ring.c
> > [...]
> > > @@ -3983,10 +3961,12 @@ int xhci_queue_isoc_tx_prepare(struct xhci_hcd *xhci, gfp_t mem_flags,
> > >       }
> > >
> > >       /* Calculate the start frame and put it in urb->start_frame. */
> > > -    if (HCC_CFC(xhci->hcc_params) &&
> > > -            ep_ring_is_processing(xhci, slot_id, ep_index)) {
> > > -        urb->start_frame = xep->next_frame_id;
> > > -        goto skip_start_over;
> > > +    if (HCC_CFC(xhci->hcc_params)) {
> > > +        if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK)
> > > +                    == EP_STATE_RUNNING &&
> > > +                !list_empty(&ep_ring->td_list))
> > > +            urb->start_frame = xep->next_frame_id;
> > > +            goto skip_start_over;
> >
> >    Forgot {}?
>
> Oh, I am sorry. I am wondering how it passed my test.
>
> I will send v3 patch soon any way.

If you are anyway making a v3 then maybe one more change,
just for readability, no (real) functional change:

if (HCC_CFC(xhci->hcc_params) && !list_empty(&ep_ring->td_list)) {
  if (le32_to_cpu(ep_...

While thinking about code cleanup I also think we should use a local variable
u32 ep_info = le32_to_cpu(ep_ctx->ep_info) as it's used several times in xhci_queue_isoc_tx_preapare(),
causing a lot of line splitting.

It should be ok as we are under the same spinlock so ep_ctx should not change.

But that is not a fix sent to a rc and stable, I can make a separate cleanup patch for it later.

-Mathias
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