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, 0 insertions, 19 deletions

diff --git a/drivers/gpu/drm/amd/display/dmub/inc/dmub_srv.h b/drivers/gpu/drm/amd/display/dmub/inc/dmub_srv.h
index f34a50dd36ea..8e23a7017588 100644
--- a/drivers/gpu/drm/amd/display/dmub/inc/dmub_srv.h
+++ b/drivers/gpu/drm/amd/display/dmub/inc/dmub_srv.h
@@ -445,25 +445,6 @@ enum dmub_status dmub_srv_cmd_queue(struct dmub_srv *dmub,
 enum dmub_status dmub_srv_cmd_execute(struct dmub_srv *dmub);
 
 /**
- * dmub_srv_cmd_submit() - submits a command to the DMUB immediately
- * @dmub: the dmub service
- * @cmd: the command to submit
- * @timeout_us: the maximum number of microseconds to wait
- *
- * Submits a command to the DMUB with an optional timeout.
- * If timeout_us is given then the service will attempt to
- * resubmit for the given number of microseconds.
- *
- * Return:
- *   DMUB_STATUS_OK - success
- *   DMUB_STATUS_TIMEOUT - wait for submit timed out
- *   DMUB_STATUS_INVALID - unspecified error
- */
-enum dmub_status dmub_srv_cmd_submit(struct dmub_srv *dmub,
-				     const struct dmub_cmd_header *cmd,
-				     uint32_t timeout_us);
-
-/**
  * dmub_srv_wait_for_auto_load() - Waits for firmware auto load to complete
  * @dmub: the dmub service
  * @timeout_us: the maximum number of microseconds to wait