[Intel-gfx] [PATCH] drm/i915: Tile F plane format support

[Ville Syrjälä]

On Tue, Sep 28, 2021 at 11:36:51PM +0300, Lisovskiy, Stanislav wrote:
> On Tue, Sep 28, 2021 at 10:02:34PM +0300, Ville Syrjälä wrote:
> > On Tue, Sep 28, 2021 at 03:49:11PM +0300, Lisovskiy, Stanislav wrote:
> > > On Mon, Sep 27, 2021 at 10:24:11PM -0700, Matt Roper wrote:
> > > > On Mon, Sep 27, 2021 at 09:29:07PM +0300, Ville Syrjälä wrote:
> > > > > On Mon, Sep 27, 2021 at 11:23:35AM -0700, Matt Roper wrote:
> > > > > > On Thu, Sep 23, 2021 at 06:49:59PM +0300, Ville Syrjälä wrote:
> > > > > > > On Thu, Sep 23, 2021 at 11:48:58AM +0300, Stanislav Lisovskiy wrote:
> > > > > > > > TileF(Tile4 in bspec) format is 4K tile organized into
> > > > > > > > 64B subtiles with same basic shape as for legacy TileY
> > > > > > > > which will be supported by Display13.
> > > > > > > 
> > > > > > > Why we still haven't done the F->tile64 rename?
> > > > > > >
> > > > > > > This is the last chance to fix this before we bake 
> > > > > > > this into the uapi and are stuck with a name that doesn't
> > > > > > > match the spec and will just confuse everyone.
> > > > > > 
> > > > > > I think you're confusing the formats here.  The bspec uses both terms
> > > > > > "TileF" and "Tile4" for the same format in different places.  There's a
> > > > > > completely different format that's referred to as both "TileS" and
> > > > > > "Tile64" in the bspec that we don't use at the moment.  So tile64
> > > > > > wouldn't be a correct rename, but tile4 could be.
> > > > > 
> > > > > Right, tile64 is the macro tile variant I think. So like Ys
> > > > > which we never bothered implementing, so I guess we''l not bother
> > > > > with tile64 either.
> > > > > 
> > > > > > 
> > > > > > In general Tile4 is much more common in the bspec than TileF is (TileF
> > > > > > terminology is mostly found in the media sections).  And bspec 44917 is
> > > > > > the most authoritative bspec page on the subject, and it refers to it as
> > > > > > Tile4, so I agree that switching over "Tile4" would probably be a good
> > > > > > move.
> > > > > > 
> > > > > > > 
> > > > > > > > 
> > > > > > ...
> > > > > > > > diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> > > > > > > > index bde5860b3686..d7dc421c6134 100644
> > > > > > > > --- a/include/uapi/drm/i915_drm.h
> > > > > > > > +++ b/include/uapi/drm/i915_drm.h
> > > > > > > > @@ -1522,7 +1522,8 @@ struct drm_i915_gem_caching {
> > > > > > > >  #define I915_TILING_NONE	0
> > > > > > > >  #define I915_TILING_X		1
> > > > > > > >  #define I915_TILING_Y		2
> > > > > > > > -#define I915_TILING_LAST	I915_TILING_Y
> > > > > > > > +#define I915_TILING_F		3
> > > > > > > > +#define I915_TILING_LAST	I915_TILING_F
> > > > > > > 
> > > > > > > fences...
> > > > > > 
> > > > > > Recognizing TileF/Tile4 separately from TileY is important to code
> > > > > > outside of display as well.  There are blitter instructions that require
> > > > > > different settings for TileY vs Tile4/F so if we drop the tracking of
> > > > > > this as a unique tiling type, it will break the blitting/copying and
> > > > > > some of the upcoming local memory support for Xe_HP-based platforms.
> > > > > 
> > > > > These are uapi definitions for set_tiling(). You are not meant to add
> > > > > anything there. Just like we didn't add anything for Yf.
> > > > 
> > > > Yeah, I think that's the real problem --- we define some values here in
> > > > the uapi header, but we also wind up using the same set of values for
> > > > driver-internal non-uapi purposes too rather than having a separate enum
> > > > (containing a superset of the uapi values) that can be used for those
> > > > other things.  Display code can use FB modifiers for some things, but
> > > > core/lmem code needs a way to refer to Tile4 and such and doesn't have a
> > > > good way to do that today.
> > > > 
> > > > I think most (all?) of the non-display code that's relying on a
> > > > definition of I915_TILING_F is in various selftests that are still being
> > > > prepared for upstreaming, so maybe there's a better way to handle the
> > > > selection of possible formats specifically in the selftest code itself.
> > > > That's really the only area of the kernel code that should need to be
> > > > aware of the specific internal layout of various buffers.
> > > 
> > > So I will proceed with the renaming at least.
> > > 
> > > Ville, suppose, I still need part of fencing related code?
> > 
> > Nah. Just nuke it all. Someone will have to fix whatever self test is
> > abusing the uapi definitions though.
> > 
> > A local #define should suffice if nothing else is deemed appropriate.
> > IIRC igt also has a local definition like this for Yf. We should
> > perhaps rename those to some igt specific namespace as well...
> 
> As Matt mentioned, removing I915_TILING_F completely is going to break
> way more than selftest, but also blitter/copy and local mem support.

No. The only non-fence use of I915_TILING_F I see is a blitter self test
of some sort.

> In fact I remember, I had to add part of those in order to get some
> tests working, another part was added by somebody else, so not even
> sure how much other stuff its going to break.
> 
> Sounds like a bit too much for simple upstreaming of the patch, we
> already had internally for more than a year, just wondering why 
> this popped up only by now.

Because someone tried to sneak in gem uapi additions under the
cover of darkness? All gem changes must be cc:dri-devel btw,
uapi doubly so. Oh, and drm_fourcc.h changes really need to go
there too.

-- 
Ville Syrjälä
Intel