Re: [PATCH 7/8] drm/i915: Fix random aux transactions failures.

Jani Nikula
2015-11-23T10:00:48Z

On Sat, 21 Nov 2015, Rodrigo Vivi <rodrigo.vivi@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.
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 35048d6..c87e937 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -905,6 +905,17 @@ 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) {
> + ret = -EBUSY;

This deserves debug logging at the very least.

BR,
Jani.

> + goto out;
> + }
> +
> if (recv_bytes > recv_size)
> recv_bytes = recv_size;

--
Jani Nikula, Intel Open Source Technology Center