Re: [PATCH] usb: xhci: Prefer endpoint context dequeue pointer over stopped_trb

[Hans de Goede]

Hi,

On 04/15/2014 09:42 PM, Julius Werner wrote:
> +hdegoede
>
> > I tried to apply this patch on top of 3.15-rc1, but it fails because of the
> > streams support added to xhci_find_new_dequeue_state()
> >
> > After some manual editing the interesting parts of
> > xhci_find_new_dequeue_state() looks like this:
> >
> > @@ -577,46 +568,57 @@ void xhci_find_new_dequeue_state(struct xhci_hcd
> > *xhci,
> >          if (ep->ep_state & EP_HAS_STREAMS) {
> >                  struct xhci_stream_ctx *ctx =
> >                          &ep->stream_info->stream_ctx_array[stream_id];
> > -               state->new_cycle_state = 0x1 &
> > le64_to_cpu(ctx->stream_ring);
> > +               hw_dequeue = le64_to_cpu(ctx->stream_ring);
> >          } else {
> >                  struct xhci_ep_ctx *ep_ctx
> >
> >                          = xhci_get_ep_ctx(xhci, dev->out_ctx, ep_index);
> > -               state->new_cycle_state = 0x1 & le64_to_cpu(ep_ctx->deq);
> > +               hw_dequeue = le64_to_cpu(ep_ctx->deq);
> >          }
> >
> > +       /* Find virtual address and segment of hardware dequeue pointer */
> >
> > +       state->new_deq_seg = ep_ring->deq_seg;
> > +       state->new_deq_ptr = ep_ring->dequeue;
> > +       while (xhci_trb_virt_to_dma(state->new_deq_seg, state->new_deq_ptr)
> > +                       != (dma_addr_t)(hw_dequeue & ~0x1)) {
> > +               next_trb(xhci, ep_ring, &state->new_deq_seg,
> > +                                       &state->new_deq_ptr);
> > +               if (state->new_deq_ptr == ep_ring->dequeue) {
> > +                       WARN_ON(1);
> > +                       return;
> > +               }
> > +       }
> >
> > Also the comparison of the dequeue pointers, using (hw_dequeue & ~0x1) might
> > have some troubles with streams. Endpoint context TR dequeue pointer LO
> > field has bits 3:1 reserved (probably zero) but stream context uses those
> > bits. Would it make sense to use (hw_dequeue & ~0xf) here instead?
>
> Ah, yes, looks like that patch wasn't in Linus' tree yet back when I
> wrote this. I think your merge looks pretty good... just use
> (hw_dequeue & ~0xf) instead of (hw_dequeue & ~0x1) to get the pointer
> as you said, and this should work fine.
>
> > But I'm still concerned about the dequeue pointer in the streams case.
> > streams may be nested, we might be pointing at another stream context
> > instead of the dequeue pointer.

Since I've not followed the entire discussion previously to this I cannot
really provide any useful feedback on this patch. Other then 2 remarks:

1) We don't use nested streams, so no need to worry about those
2) You're right that for streams to get the dequeue address you need
to mask with ~0xf

Regards,

Hans
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