On Mon, May 11, 2026 at 09:50:59AM -0300, Gustavo Sousa wrote:
> Imre Deak <[email protected]> writes:
>
> > On Mon, May 11, 2026 at 09:20:56AM -0300, Gustavo Sousa wrote:
> >> James Xiong <[email protected]> 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 <[email protected]>
> >>
> >> +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.
AFAIU stable rules require knowing that a fix fixes something for a
user. I suppose one way to make this sure would be reproducing a problem
with PIPE DMC explicitly enabled early, before the firmware is loaded.
> That said, I'm not very involved in that, so I can say for sure.
>
> --
> 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 <[email protected]>
> >>
> >> > ---
> >> > 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
