Re: [PATCH v4 5/8] drm/i915: Bump gen4+ fb stride limit to 256KiB

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH v4 5/8] drm/i915: Bump gen4+ fb stride limit to 256KiB
Date: Wed, 30 Jan 2019 16:33:18 +0200	[thread overview]
Message-ID: <20190130143318.GM20097@intel.com> (raw)
In-Reply-To: <154884246429.21797.7010460588091657462@skylake-alporthouse-com>

On Wed, Jan 30, 2019 at 10:01:04AM +0000, Chris Wilson wrote:
> Quoting Daniel Vetter (2019-01-30 09:58:56)
> > On Thu, Jan 24, 2019 at 08:59:36PM +0200, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > With gtt remapping plugged in we can simply raise the stride
> > > limit on gen4+. Let's just pick the limit to match the render
> > > engine max stride (256KiB).
> > > 
> > > No remapping CCS because the virtual address of each page actually
> > > matters due to the new hash mode
> > > (WaCompressedResourceDisplayNewHashMode:skl,kbl etc.), and no
> > > remapping on gen2/3 due extra complications from fence alignment
> > > and gen2 2KiB GTT tile size. Also no real benefit since the
> > > display engine limits already match the other limits.
> > > 
> > > v2: Rebase due to is_ccs_modifier()
> > > v3: Tweak the comment and commit msg
> > > 
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > 
> > > ---
> > >  drivers/gpu/drm/i915/intel_display.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > > index 3713b6f1796e..e0cf43336b62 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -2470,6 +2470,15 @@ static
> > >  u32 intel_fb_max_stride(struct drm_i915_private *dev_priv,
> > >                       u32 pixel_format, u64 modifier)
> > >  {
> > > +     /*
> > > +      * Arbitrary limit for gen4+ chosen to match the
> > > +      * render engine max stride.
> > > +      *
> > > +      * The new CCS hash mode makes remapping impossible
> > > +      */
> > > +     if (INTEL_GEN(dev_priv) >= 4 && !is_ccs_modifier(modifier))
> > > +             return 256*1024;
> > 
> > bikeshed: KB(256) but I'm not sure how much we use these really.
> 
> Polka-dot bikeshed: SZ_256K

I tried a cocci conversion to these, but ended up being slightly
annoyed by the fact that we only have defines for POT sizes, and
there are quite a few non-POT sizes in the code.

-- 
Ville Syrjälä
Intel
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