[PATCH 1/1] drm/i915/gsc: Fix the Driver-FLR completion

[Teres Alexis, Alan Previn]

Thanks for reviewing - sounds good - will fix those comments up as per your recommendation.

On Fri, 2023-01-20 at 11:14 +0200, Jani Nikula wrote:
> On Thu, 19 Jan 2023, Alan Previn <alan.previn.teres.alexis at intel.com> wrote:
> > The Driver-FLR flow may inadvertently exit early before the full
> > completion of the re-init of the internal HW state if we only poll
> > GU_DEBUG Bit31 (polling for it to toggle from 0 -> 1). Instead
> > we need a two-step completion wait-for-completion flow that also
> > involves GU_CNTL. See the patch and new code comments for detail.
> > This is new direction from HW architecture folks.
> > 
> > Signed-off-by: Alan Previn <alan.previn.teres.alexis at intel.com>
> > Fixes: 5a44fcd73498 ("drm/i915/gsc: Do a driver-FLR on unload if GSC was loaded")
> > ---
> >  drivers/gpu/drm/i915/intel_uncore.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > index 8dee9e62a73e..959869e2ff05 100644
> > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > @@ -2748,6 +2748,12 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
> >         /* Trigger the actual Driver-FLR */
> >         intel_uncore_rmw_fw(uncore, GU_CNTL, 0, DRIVERFLR);
> >  
> > +       /* Completion Step 1 - poll for 'CNTL-BIT31 = 0' wait for hw teardown to complete */
> 
> Please don't use comments to repeat what the code already says.
> 
> Here, you could just say, "Wait for hardware teardown to complete",
> which describes what the code does at a higher level, but does not
> duplicate any of it.
> 
> > +       ret = intel_wait_for_register_fw(uncore, GU_CNTL,
> > +                                        DRIVERFLR_STATUS, 0,
> > +                                        flr_timeout_ms);
> > +
> > +       /* Completion: Step 2 - poll for 'DEBUG-BIT31 = 1' for hw/fw re-init to complete */
> 
> "Wait for hardware/firmware re-init to complete"
> 
> >         ret = intel_wait_for_register_fw(uncore, GU_DEBUG,
> >                                          DRIVERFLR_STATUS, DRIVERFLR_STATUS,
> >                                          flr_timeout_ms);
> > @@ -2756,6 +2762,7 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
> >                 return;
> >         }
> >  
> > +       /* Write 1 to clear GU_DEBUG's sticky completion status bit */
> 
> "Clear sticky completion status" maybe?
> 
> >         intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
> >  }
> >  
> > 
> > base-commit: 0a0ee61784df01ac098a92bd43673ee30c629f13
>