[Intel-gfx] [PATCH igt 1/3] lib/igt_fb: also call __gem_set_tiling for Y tiling

[Ville Syrjälä]

On Mon, Feb 01, 2016 at 05:44:42PM +0000, Tvrtko Ursulin wrote:
> 
> On 01/02/16 17:16, Zanoni, Paulo R wrote:
> > Em Sex, 2016-01-29 às 21:06 +0200, Ville Syrjälä escreveu:
> >> On Fri, Jan 29, 2016 at 04:46:30PM -0200, Paulo Zanoni wrote:
> >>> The interesting thing is that if we don't do this, we still get a
> >>> Y tiled framebuffer, but there won't be a fence around it, which
> >>> makes
> >>> the GTT mmaps less interesting. Is this a Kernel bug?
> >>
> >> I think some tests currently depend on not having a fence for Y tiled
> >> fbs. So this could break stuff.
> >
> > Do you have any additional information that could help me discover
> > which ones? A quick look on the IGT tests mentioning tiling didn't
> > point anything obvious.
> >
> > Besides, I think it's probably not a good idea to have such a high
> > level helper function behaving differently depending on the tiling
> > type, I'd vote to either call set_tiling on both or on none.
> 
> Noticed the thread by accident. :)
> 
> I can't help with the question of which tests might be affected by this. 
> Some low level ones like kms_addfb don't use the fb helpers so they 
> shouldn't be. Can't remember if any other would be.
> 
> But just a little bit of background:
> 
> Basically with the introduction of Y tiled (and Yf) scanout in Gen9 we 
> have forked the path and destroyed the coupling between obj->tiling and 
> framebuffer tiling.
> 
> The X special casing in create_bo_for_fb is for compatibility with old 
> userspace, but going forward it was decided fb  modifiers should be used 
> to tell the driver about tiling and get/set_tiling ioctl is about 
> fencing and only that.
> 
> Paths implemented in IGT back then were rendering to Y and Yf tiling fbs 
> via a temporary linear surface which is then blitted (blit?) to the real 
> fb obj. (With the blitter doing the appropriate transformation.)
> 
> So in that respect adding Y tiling to create_bo_for_fb would be wrong 
> because it is not aligned with the above, and also you cannot support Yf 
> this way at all.
> 
> But I do agree this creates a problem for some use cases within the IGT 
> since the fb and backing obj are created atomically and once that is 
> done you cannot fiddle with obj->tiling (aka fencing).

I suppose we could either make it easier to create the obj and fb
separately, or we could add a parameter to the fb funcs to indicate
whether we want a fence or not.

-- 
Ville Syrjälä
Intel OTC