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

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

Gustavo Sousa <gustavo.sousa@intel.com> writes:

> Imre Deak <imre.deak@intel.com> writes:
>
>> On Mon, May 11, 2026 at 09:20:56AM -0300, Gustavo Sousa wrote:
>>> James Xiong <james.xiong@intel.com> writes:
>>> 
>>> > 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>
>>> 
>>> +Imre
>>> 
>>> Perhaps this deserves a fixes tag?
>>
>> Since that would result in backporting the fix to -stable, it depends on
>> whether enabling the pipe DMC functionality before the firmware is
>> loaded is an actual functionality problem.
>
> I think we depend on pipe DMC for the flip queue functionality, so I
> suspect it could be an issue.  That said, I'm not very involved in that,
> so I can say for sure.

s/can/can not/

--
Gustavo Sousa

>
> --
> Gustavo Sousa
>
>>
>>> If so, maybe it should be this one:
>>> 
>>> Fixes: 3af2ff0840be ("drm/i915: Enable a PIPEDMC whenever its corresponding pipe is enabled")
>>> 
>>> The change itself looks good to me, so
>>> 
>>> Reviewed-by: Gustavo Sousa <gustavo.sousa@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