Re: [PATCH v2] drm/i915/dmc: fix assert_dmc_loaded WARN during async firmware load

[Gustavo Sousa <gustavo.sousa@intel.com>]

Jani Nikula <jani.nikula@linux.intel.com> writes:

> On Thu, 07 May 2026, James Xiong <james.xiong@intel.com> wrote:
>> 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.
>
> I wonder if intel_dmc_enable_pipe() should call intel_dmc_wait_fw_load()
> itself?

I also though about that, but, if you need to call
intel_dmc_wait_fw_load() in a regular modeset flow, wouldn't that be a
symptom of a bug?

--
Gustavo Sousa

>
>>
>> v2: Fix by calling intel_dmc_wait_fw_load() in
>>     intel_modeset_setup_hw_state() before iterating the CRTCs (Gustavo
>>     Sousa).
>>
>> Signed-off-by: James Xiong <james.xiong@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_modeset_setup.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_modeset_setup.c b/drivers/gpu/drm/i915/display/intel_modeset_setup.c
>> index e88082c8caac..277e56848470 100644
>> --- a/drivers/gpu/drm/i915/display/intel_modeset_setup.c
>> +++ b/drivers/gpu/drm/i915/display/intel_modeset_setup.c
>> @@ -961,6 +961,8 @@ void intel_modeset_setup_hw_state(struct intel_display *display,
>>  	 * intel_sanitize_plane_mapping() may need to do vblank
>>  	 * waits, so we need vblank interrupts restored beforehand.
>>  	 */
>> +	intel_dmc_wait_fw_load(display);
>> +
>
> No matter what, the comment above now appears to refer to this
> intel_dmc_wait_fw_load() call, which makes no sense at all.
>
> BR,
> Jani.
>
>>  	for_each_intel_crtc(display->drm, crtc) {
>>  		struct intel_crtc_state *crtc_state =
>>  			to_intel_crtc_state(crtc->base.state);
>
> -- 
> Jani Nikula, Intel