Re: [Intel-gfx] [PATCH 1/5] drm/i915/fbc: Remove ancient 16k plane stride limit

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Matt Roper <matthew.d.roper@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 1/5] drm/i915/fbc: Remove ancient 16k plane stride limit
Date: Fri, 15 Sep 2023 19:54:00 +0300	[thread overview]
Message-ID: <ZQSMKGTxsKlqhUBZ@intel.com> (raw)
In-Reply-To: <20230915164854.GA2706891@mdroper-desk1.amr.corp.intel.com>

On Fri, Sep 15, 2023 at 09:48:54AM -0700, Matt Roper wrote:
> On Thu, Sep 14, 2023 at 02:38:50PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > The 16k max plane stride limit seems to be originally from
> > i965gm, and no limit explicit limit has been specified since (g4x+).
> 
> There are maximum limits specified on the PLANE_STRIDE register pages
> (bspec 7667, 50416, 69877).
> 
> display version 9 - 10:   max 8k pixels and 32k bytes
> display version 11 - 12:  max 8k pixels
> display version 13 - 20:  max 128k bytes

Sure, but those are handled elsewhere. Here we're only
interested in limits specific to FBC.

> 
> 
> Matt
> 
> > So let's assume the max plane stride itself is a suitable limit
> > also for the more recent FBC hardware.
> > 
> > In fact even for i965gm the max X-tiled stride is also 16k so
> > technically we don't need the check there either, but let's
> > keep it there anyway since it's explicitly mentioned in the
> > spec. Gen2/3 have more strict limits checked separately.
> > 
> > Cc: Swati Sharma <swati2.sharma@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_fbc.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> > index 817e5784660b..1b3358a0fbfb 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> > @@ -866,7 +866,8 @@ static bool stride_is_valid(const struct intel_plane_state *plane_state)
> >  	if (DISPLAY_VER(i915) == 2 || DISPLAY_VER(i915) == 3)
> >  		return stride == 4096 || stride == 8192;
> >  
> > -	if (DISPLAY_VER(i915) == 4 && !IS_G4X(i915) && stride < 2048)
> > +	if (DISPLAY_VER(i915) == 4 && !IS_G4X(i915) &&
> > +	    (stride < 2048 || stride > 16384))
> >  		return false;
> >  
> >  	/* Display WA #1105: skl,bxt,kbl,cfl,glk */
> > @@ -874,9 +875,6 @@ static bool stride_is_valid(const struct intel_plane_state *plane_state)
> >  	    fb->modifier == DRM_FORMAT_MOD_LINEAR && stride & 511)
> >  		return false;
> >  
> > -	if (stride > 16384)
> > -		return false;
> > -
> >  	return true;
> >  }
> >  
> > -- 
> > 2.41.0
> > 
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> Linux GPU Platform Enablement
> Intel Corporation

-- 
Ville Syrjälä
Intel