drm/amd/display: Flush framebuffer data before passing to DMCUB

[Why]
There's a data race that can occur between when we update the
inbox write pointer vs when the memory for the command actually gets
flushed from the map to the framebuffer.

DMCUB can read stale or partially invalid data when this race occurs.

[How]
Before updating the write pointer we can read back all pending commands
to ensure that we stall for the writes to be flushed to framebuffer.

We don't need to worry about choosing HDP vs VM flush with this
mechanism.

Drop the dmub_srv_cmd_submit() while we're updating this to work
correctly since nothing was actually using this API and the caller
should be explicit about the API flow here - by doing this on execute
we can give some extra time for the flush to finish while
preparing other commands.

We should try to avoid writing single commands
because of this overhead.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 7 insertions, 23 deletions

diff --git a/drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c b/drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c
index 9a959f871f11..23ca1fe97757 100644
--- a/drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c
+++ b/drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c
@@ -405,33 +405,17 @@ enum dmub_status dmub_srv_cmd_execute(struct dmub_srv *dmub)
 	if (!dmub->hw_init)
 		return DMUB_STATUS_INVALID;
 
+	/**
+	 * Read back all the queued commands to ensure that they've
+	 * been flushed to framebuffer memory. Otherwise DMCUB might
+	 * read back stale, fully invalid or partially invalid data.
+	 */
+	dmub_rb_flush_pending(&dmub->inbox1_rb);
+
 	dmub->hw_funcs.set_inbox1_wptr(dmub, dmub->inbox1_rb.wrpt);
 	return DMUB_STATUS_OK;
 }
 
-enum dmub_status dmub_srv_cmd_submit(struct dmub_srv *dmub,
-				     const struct dmub_cmd_header *cmd,
-				     uint32_t timeout_us)
-{
-	uint32_t i = 0;
-
-	if (!dmub->hw_init)
-		return DMUB_STATUS_INVALID;
-
-	for (i = 0; i <= timeout_us; ++i) {
-		dmub->inbox1_rb.rptr = dmub->hw_funcs.get_inbox1_rptr(dmub);
-		if (dmub_rb_push_front(&dmub->inbox1_rb, cmd)) {
-			dmub->hw_funcs.set_inbox1_wptr(dmub,
-						       dmub->inbox1_rb.wrpt);
-			return DMUB_STATUS_OK;
-		}
-
-		udelay(1);
-	}
-
-	return DMUB_STATUS_TIMEOUT;
-}
-
 enum dmub_status dmub_srv_wait_for_auto_load(struct dmub_srv *dmub,
 					     uint32_t timeout_us)
 {