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

[Brian Starkey]

Hi Ville,

On Thu, Feb 22, 2018 at 11:42:29PM +0200, 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.

I totally agree that this is a good idea, but...

>
>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>
>---
> 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];

Isn't changing the type liable to break something for someone?

Thanks,
-Brian

> };
>
> struct drm_color_lut {
>-- 
>2.16.1
>