Re: [PATCH 01/13] drm/i915/vrr: Fix intel_vrr_dcb_vmin_vblank_start()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Oct 27, 2026 at 06:04:39PM +0200, Jani Nikula wrote:
> On Fri, 23 Oct 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > intel_vrr_dcb_vmin_vblank_start() may evaluate
> > intel_vrr_dcb_vmin_vblank_start_next() twice, and given that
> > this is doing hardware access under the hood isn't really
> > desired.
> 
> Feels like there's a word missing there. This? It?

One of those, yes.

> 
> > Even worse, the double evaluation might even cause
> > intel_vrr_dcb_vmin_vblank_start() itself to finally
> > return -EINVAL (if we race against the DMC hard enough),
> > which we definitely never want to do.
> >
> > Eliminate the double evaluation, guaranteeing a sane
> > final return value at the same time.
> 
> I think a Fixes: would be in order.

Fixes: c4aba65c26fd ("drm/i915/display: Wait for VRR PUSH status
update")

although the whole DC balance stuff is currently disabled 
due to other issues.

> 
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> 
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_vrr.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> > index b14750692ae0..e59345bd1d33 100644
> > --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> > @@ -1202,9 +1202,13 @@ int intel_vrr_safe_window_start(const struct intel_crtc_state *crtc_state)
> >  static int
> >  intel_vrr_dcb_vmin_vblank_start(const struct intel_crtc_state *crtc_state)
> >  {
> > -	return (intel_vrr_dcb_vmin_vblank_start_next(crtc_state) < 0) ?
> > -		intel_vrr_dcb_vmin_vblank_start_final(crtc_state) :
> > -		intel_vrr_dcb_vmin_vblank_start_next(crtc_state);
> > +	int vblank_start;
> > +
> > +	vblank_start = intel_vrr_dcb_vmin_vblank_start_next(crtc_state);
> > +	if (vblank_start < 0)
> > +		vblank_start = intel_vrr_dcb_vmin_vblank_start_final(crtc_state);
> > +
> > +	return vblank_start;
> >  }
> >  
> >  int intel_vrr_vmin_safe_window_end(const struct intel_crtc_state *crtc_state)
> 
> -- 
> Jani Nikula, Intel

-- 
Ville Syrjälä
Intel