Re: [igt-dev] [PATCH i-g-t 1/2] lib/igt_fb: Don't use blitter for large buffers

[Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>]

On Thu, 2019-03-28 at 18:25 +0000, Chris Wilson wrote:
> Quoting Ville Syrjala (2019-03-28 17:54:49)
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > The blitter stride is limited to <32k. Fall back to gtt mmap or
> > rendercopy if we're about to exceed that.
> > 
> > Not quite sure why we're not just using gtt mmap for Y tiling
> > always. But let's keep it like that for now.
> > 
> > v2: Use rendercopy as the fallback for Yf
> > 
> > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  lib/igt_fb.c | 25 ++++++++++++++++++-------
> >  1 file changed, 18 insertions(+), 7 deletions(-)
> > 
> > diff --git a/lib/igt_fb.c b/lib/igt_fb.c
> > index fcd7c4c5d187..8b6adf55a338 100644
> > --- a/lib/igt_fb.c
> > +++ b/lib/igt_fb.c
> > @@ -1502,6 +1502,20 @@ struct fb_blit_upload {
> >         struct intel_batchbuffer *batch;
> >  };
> >  
> > +static bool use_rendercopy(const struct igt_fb *fb)
> > +{
> > +       return is_ccs_modifier(fb->modifier) ||
> > +               (fb->modifier == I915_FORMAT_MOD_Yf_TILED &&
> > +                fb->strides[0] >= 32768);
> 
> And probably wise to assert <= 256k.
Is that a hardware limitation for the render engine?

> 
> > +
> > +static bool use_blitter(const struct igt_fb *fb)
> > +{
> > +       return (fb->modifier == I915_FORMAT_MOD_Y_TILED ||
> > +               fb->modifier == I915_FORMAT_MOD_Yf_TILED) &&
> > +               fb->strides[0] < 32768;
> 
> 32k dwords is the limit for tiled blits (on gen4+). I presume strides[]
> is in bytes.

I see conflicting limits in bspec for this, the Data Size Limitations page says
"up to 32,768 bytes per scan line" whereas the docs for XY_SRC_COPY_BLT claims
32k dwords.





> -Chris
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