> -----Original Message-----
> From: Daniel Vetter <daniel@xxxxxxxx>
> Sent: Monday, May 4, 2020 2:17 PM
> To: Kahola, Mika <mika.kahola@xxxxxxxxx>
> Cc: dri-devel <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH] uapi/drm/drm_fourcc.h: Note on platform specificity for
> format modifiers
>
> On Mon, May 4, 2020 at 11:08 AM Mika Kahola <mika.kahola@xxxxxxxxx>
> wrote:
> >
> > Make an additional note on DRM format modifiers for x and y tiling.
> > These format modifiers are defined for BDW+ platforms and therefore
> > definition is not valid for older gens. This is due to address
> > swizzling for tiled surfaces is no longer used. For newer platforms
> > main memory controller has a more effective address swizzling algorithm.
> >
> > Signed-off-by: Mika Kahola <mika.kahola@xxxxxxxxx>
> > ---
> > include/uapi/drm/drm_fourcc.h | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/drm/drm_fourcc.h
> > b/include/uapi/drm/drm_fourcc.h index 8bc0b31597d8..3e56c24cabb6
> > 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -356,7 +356,8 @@ extern "C" {
> > *
> > * This format is highly platforms specific and not useful for cross-driver
> > * sharing. It exists since on a given platform it does uniquely
> > identify the
> > - * layout in a simple way for i915-specific userspace.
> > + * layout in a simple way for i915-specific userspace. The format is
> > + * ill-defined for platforms older than BDW.
>
> Hm this is a bit confusing, since you're just adding a new sentences and not
> really clarifying the paragraph overall. Right above we have the detailed
> description of the modifier on gen8+, I'd replace the entire paragraph here with
> something like:
>
> "Note that this layout is only accurate on intel gen 8+ or valleyview chipsets. On
> earlier platforms the is highly platforms specific and not useful for cross-driver
> sharing. It exists since on a given platform it does uniquely identify the layout in
> a simple way for i915-specific userspace, which facilitated conversion of
> userspace to modifiers. Additionally the exact format on some really old
> platforms is not known."
>
> That way it's much clearer that the specification is well-defined and where, with
> the old stuff as exceptions. Your patch kinda makes bdw+ the exception of the
> exception, and that's hard to understand.
I admit, that the wording may have been confusing. I'll update the patch with your proposal.
Cheers,
Mika
>
> Cheers, Daniel
>
>
>
> > */
> > #define I915_FORMAT_MOD_X_TILED fourcc_mod_code(INTEL, 1)
> >
> > @@ -371,7 +372,8 @@ extern "C" {
> > *
> > * This format is highly platforms specific and not useful for cross-driver
> > * sharing. It exists since on a given platform it does uniquely
> > identify the
> > - * layout in a simple way for i915-specific userspace.
> > + * layout in a simple way for i915-specific userspace. The format is
> > + * ill-defined for platforms older than BDW.
> > */
> > #define I915_FORMAT_MOD_Y_TILED fourcc_mod_code(INTEL, 2)
> >
> > --
> > 2.20.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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