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

[Paulo Zanoni]

2015-12-07 10:04 GMT-02:00 Rodrigo Vivi <rodrigo.vivi at intel.com>:
> 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.
> v3: This patch is crucial to make PSR test cases reliably working
>     on SKL. So split this patch from the aux re-org series and add
>     a FIXME as a promisse to continue that effort besides reminding
>     to remove the sleep when that is merged.
> v4: Use a bigger usleep range so kernel doesn't need to be interrupted
>     on a exact time, as suggested by Paulo.
>     But anyway we should discuss the better time
>     ranges on the EBUSY handle re-org at drm level since this one here
>     is temporary.
>
> Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> 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
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index f335c92..0d5fe80 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -915,6 +915,27 @@ 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);
> +               /*
> +                * FIXME: This patch was created on top of a series that
> +                * organize the retries at drm level. There EBUSY should
> +                * also take care for 1ms wait before retrying.
> +                * That aux retries re-org is still needed and after that is
> +                * merged we remove this sleep from here.
> +                */
> +               usleep_range(1000,1500);

s/1000,1500/1000, 1500/

Although I'm not so sure why 1ms. Shouldn't we stick to the spec
default of 400 or Ville's default of 500?

Anyway, having this seems better than not having this, and the
possible problems are highlighted by the FIXME so, with or without
changes:
Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

> +               ret = -EBUSY;
> +               goto out;
> +       }
> +
>         if (recv_bytes > recv_size)
>                 recv_bytes = recv_size;
>
> --
> 2.4.3
>
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-- 
Paulo Zanoni