> -----Original Message-----
> From: Pekka Paalanen <pekka.paala...@collabora.com>
> Sent: Monday, June 16, 2025 7:02 PM
> To: Borah, Chaitanya Kumar <chaitanya.kumar.bo...@intel.com>
> Cc: Alex Hung <alex.h...@amd.com>; dri-de...@lists.freedesktop.org; amd-
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> <uma.shan...@intel.com>; quic_nas...@quicinc.com;
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> Subject: Re: [PATCH V9 16/43] drm/colorop: Add 3x4 CTM type
>
> On Mon, 16 Jun 2025 11:30:23 +0000
> "Borah, Chaitanya Kumar" <chaitanya.kumar.bo...@intel.com> wrote:
>
> > > -----Original Message-----
> > > From: Alex Hung <alex.h...@amd.com>
> > > Sent: Wednesday, April 30, 2025 6:41 AM
> > > To: dri-de...@lists.freedesktop.org; amd-...@lists.freedesktop.org
> > > Cc: wayland-devel@lists.freedesktop.org; harry.wentl...@amd.com;
> > > alex.h...@amd.com; leo....@amd.com; ville.syrj...@linux.intel.com;
> > > pekka.paala...@collabora.com; cont...@emersion.fr; m...@igalia.com;
> > > jad...@redhat.com; sebastian.w...@redhat.com;
> > > shashank.sha...@amd.com; ago...@nvidia.com; jos...@froggi.es;
> > > mdaen...@redhat.com; aleix...@kde.org; xaver.h...@gmail.com;
> > > victo...@system76.com; dan...@ffwll.ch; Shankar, Uma
> > > <uma.shan...@intel.com>; quic_nas...@quicinc.com;
> > > quic_cbr...@quicinc.com; quic_abhin...@quicinc.com;
> > > mar...@marcan.st; liviu.du...@arm.com; sashamcint...@google.com;
> > > Borah, Chaitanya Kumar <chaitanya.kumar.bo...@intel.com>;
> > > louis.chau...@bootlin.com; Daniel Stone <dani...@collabora.com>
> > > Subject: [PATCH V9 16/43] drm/colorop: Add 3x4 CTM type
> > >
> > > From: Harry Wentland <harry.wentl...@amd.com>
> > >
> > > This type is used to support a 3x4 matrix in colorops. A 3x4 matrix
> > > uses the last column as a "bias" column. Some HW exposes support for
> > > 3x4. The calculation looks like:
> > >
> > > out matrix in
> > > |R| |0 1 2 3 | | R |
> > > |G| = |4 5 6 7 | x | G |
> > > |B| |8 9 10 11| | B |
> > > |1.0|
> > >
> > > This is also the first colorop where we need a blob property to
> > > program the property. For that we'll introduce a new DATA property
> > > that can be used by all colorop TYPEs requiring a blob. The way a
> > > DATA blob is read depends on the TYPE of the colorop.
> > >
> > > We only create the DATA property for property types that need it.
> >
> > Is there any value to adding pre-offsets [1] in the uapi?
> >
> > |R/Cr| | c0 c1 c2 | ( |R/Cr| |preoff0| ) |postoff0|
> > |G/Y | = | c3 c4 c5 | x ( |G/Y | + |preoff1| ) + |postoff1|
> > |B/Cb| | c6 c7 c8 | ( |B/Cb| |preoff2| ) |postoff2|
> >
> > Handling limited range values is one use case that I can think of.
>
> Hi,
>
> in the mathematical sense, no. A pre-offset can always be converted into a
> post-offset by multiplying it with the 3x3 matrix (and adding to the existing
> post-offset). This can be pre-computed, no need to do it separately for every
> pixel.
>
> For hardware reasons, I have no idea.
Thank you for the reply, Pekka. Our hardware does allow programming Pre-offsets
separately.
Currently I can't think of a particular advantage of that if mathematically a
post-offset does the job but I will keep this thread posted if I find something
out.
Regards
Chaitanya
>
> > [1]
> > https://cgit.freedesktop.org/drm-tip/tree/drivers/gpu/drm/i915/display
> > /intel_color.c#n112
> >
>
> Thanks,
> pq
