[Intel-gfx] [PATCH 1/4] drm/uapi: The ctm matrix uses sign-magnitude representation

[Daniel Vetter]

On Fri, Feb 23, 2018 at 11:26:41AM -0500, Harry Wentland wrote:
> On 2018-02-22 04:42 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > The documentation for the ctm matrix suggests a two's complement
> > format, but at least the i915 implementation is using sign-magnitude
> > instead. And looks like malidp is doing the same. Change the docs
> > to match the current implementation, and change the type from __s64
> > to __u64 to drive the point home.
> > 
> > Cc: dri-devel at lists.freedesktop.org
> > Cc: Mihail Atanassov <mihail.atanassov at arm.com>
> > Cc: Liviu Dudau <liviu.dudau at arm.com>
> > Cc: Brian Starkey <brian.starkey at arm.com>
> > Cc: Mali DP Maintainers <malidp at foss.arm.com>
> > Cc: Johnson Lin <johnson.lin at intel.com>
> > Cc: Uma Shankar <uma.shankar at intel.com>
> > Cc: Shashank Sharma <shashank.sharma at intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Good clarification. Our new CTM implementation (1) actually assumed
> two's complement but nobody's using it yet, so we'll patch it to
> convert.

Another reason to start looking into igt and the tests there? That would
have caught this too ...
-Daniel

> 
> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
> 
> (1) https://patchwork.freedesktop.org/patch/204005/
> 
> Harry
> 
> > ---
> >  include/uapi/drm/drm_mode.h | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index 2c575794fb52..b5d7d9e0eff5 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -598,8 +598,11 @@ struct drm_mode_crtc_lut {
> >  };
> >  
> >  struct drm_color_ctm {
> > -	/* Conversion matrix in S31.32 format. */
> > -	__s64 matrix[9];
> > +	/*
> > +	 * Conversion matrix in S31.32 sign-magnitude
> > +	 * (not two's complement!) format.
> > +	 */
> > +	__u64 matrix[9];
> >  };
> >  
> >  struct drm_color_lut {
> > 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch