drm: aux ->transfer() can return 0, deal with it

vsyrjala · airlied · commit a1f5524a66ff · 2016-07-29T14:13:03.000+10:00
Restore the correct behaviour (as in check msg.reply) when aux ->transfer() returns 0. It got removed in commit 82922da ("drm/dp_helper: Retry aux transactions on all errors") Now I can actually dump the "entire" DPCD on a Dell UP2314Q with ddrescue. It has some offsets in the DPCD that can't be read for some resaon, all you get is defers. Previously ddrescue would just give up at the first unredable offset on account of read() returning 0 means EOF. Here's the ddrescue log for the interested: 0x00000000 0x00001400 + 0x00001400 0x00000030 - 0x00001430 0x000001D0 + 0x00001600 0x00000030 - 0x00001630 0x0001F9D0 + 0x00021000 0x00000001 - 0x00021001 0x000DEFFF + Cc: Lyude <cpaul@redhat.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch Cc: stable@vger.kernel.org Fixes: 82922da ("drm/dp_helper: Retry aux transactions on all errors") Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
@@ -203,7 +203,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 
 		ret = aux->transfer(aux, &msg);
 
-		if (ret > 0) {
+		if (ret >= 0) {
 			native_reply = msg.reply & DP_AUX_NATIVE_REPLY_MASK;
 			if (native_reply == DP_AUX_NATIVE_REPLY_ACK) {
 				if (ret == size)
