[Intel-gfx] [PATCH 7/9] drm/i915: Fix random aux transactions failures.

[Rodrigo Vivi]

Hi Jani,

Is this version ok now?
Do you believe we could go only with this patch for now and continue the
retry and kill read_wake function later?

Thanks,
Rodrigo.

On Wed, Nov 25, 2015 at 4:04 PM Rodrigo Vivi <rodrigo.vivi at intel.com> wrote:

> Mainly aux communications on sink_crc
> were failing a lot randomly on recent platforms.
> The first solution was to try to use intel_dp_dpcd_read_wake, but then
> it was suggested to move retries to drm level.
>
> Since drm level was already taking care of retries and didn't want
> to through random retries on that level the second solution was to
> put the retries at aux_transfer layer what was nacked.
>
> So I realized we had so many retries in different places and
> started to organize that a bit. During this organization I noticed
> that we weren't handing at all the case were the message size was
> zeroed. And this was exactly the case that was affecting sink_crc.
>
> Also we weren't respect BSPec who says this size message = 0 or > 20
> are forbidden.
>
> It is a fact that we still have no clue why we are getting this
> forbidden value there. But anyway we need to handle that for now
> so we return -EBUSY and drm level takes care of the retries that
> are already in place.
>
> v2: Print debug messsage when this case is reached as suggested
>     by Jani.
>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Tested-by: Daniel Stone <daniels at collabora.com> # SKL
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c
> b/drivers/gpu/drm/i915/intel_dp.c
> index 54e85f5..a02bfa1 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -899,6 +899,19 @@ done:
>         /* Unload any bytes sent back from the other side */
>         recv_bytes = ((status & DP_AUX_CH_CTL_MESSAGE_SIZE_MASK) >>
>                       DP_AUX_CH_CTL_MESSAGE_SIZE_SHIFT);
> +
> +       /*
> +        * By BSpec: "Message sizes of 0 or >20 are not allowed."
> +        * We have no idea of what happened so we return -EBUSY so
> +        * drm layer takes care for the necessary retries.
> +        */
> +       if (recv_bytes == 0 || recv_bytes > 20) {
> +               DRM_DEBUG_KMS("Forbidden recv_bytes = %d on aux
> transaction\n",
> +                             recv_bytes);
> +               ret = -EBUSY;
> +               goto out;
> +       }
> +
>         if (recv_bytes > recv_size)
>                 recv_bytes = recv_size;
>
> --
> 2.4.3
>
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