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

[Teres Alexis, Alan Previn]

Forwarded offline. Let's hold off R-B or merging until I verify that hw spec update is finalized to be exactly as what this patch is (probably a minor delay).

On Thu, 2023-01-19 at 14:57 -0500, Vivi, Rodrigo wrote:
> On Thu, Jan 19, 2023 at 11:49:55AM -0800, Alan Previn 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.
> 
> Do we have this documented anywhere?
> 
> but the patch looks good to me...
> 
> > 
> > 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 */
> > +       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 */
> >         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 */
> >         intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
> >  }
> >  
> > 
> > base-commit: 0a0ee61784df01ac098a92bd43673ee30c629f13
> > -- 
> > 2.39.0
> >