[PATCH v3] drm/i915/dmc: fix assert_dmc_loaded WARN during async firmware load

[James Xiong <james.xiong@intel.com>]

During driver probe, DMC firmware is loaded asynchronously via a
workqueue. There is a race between parse_dmc_fw() setting the payload
pointer (making has_dmc_id_fw() return true) and intel_dmc_load_program()
writing the firmware to hardware registers. If the probe thread calls
intel_dmc_enable_pipe() -> assert_dmc_loaded() in this window via
intel_modeset_setup_hw_state(), it sees parsed payload but stale HW
registers, triggering a ~20% intermittent WARNING on ADL-N warm boot.

v2: Fix by calling intel_dmc_wait_fw_load() in
    intel_modeset_setup_hw_state() before iterating the CRTCs (Gustavo
    Sousa).

v3: Move intel_dmc_wait_fw_load() into intel_dmc_enable_pipe() itself
    so the function is self-contained (Jani Nikula, Gustavo Sousa).

Signed-off-by: James Xiong <james.xiong@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dmc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
index 0df4f42ba3e3..4151eae92744 100644
--- a/drivers/gpu/drm/i915/display/intel_dmc.c
+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
@@ -786,7 +786,12 @@ void intel_dmc_enable_pipe(const struct intel_crtc_state *crtc_state)
 	enum pipe pipe = crtc->pipe;
 	enum intel_dmc_id dmc_id = PIPE_TO_DMC_ID(pipe);
 
-	if (!is_valid_dmc_id(dmc_id) || !has_dmc_id_fw(display, dmc_id))
+	if (!is_valid_dmc_id(dmc_id))
+		return;
+
+	intel_dmc_wait_fw_load(display);
+
+	if (!has_dmc_id_fw(display, dmc_id))
 		return;
 
 	if (!can_enable_pipedmc(crtc_state)) {
-- 
2.34.1