@@ -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(1000,1000);
+ ret = -EBUSY;
+ goto out;
+ }
+
if (recv_bytes > recv_size)
recv_bytes = recv_size;
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. Cc: Jani Nikula <jani.nikula@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com> Tested-by: Daniel Stone <daniels@collabora.com> # SKL Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com> --- drivers/gpu/drm/i915/intel_dp.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+)