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

[Harry Wentland]

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.

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 {
>