Re: [PATCH 2/3] drm/komeda: Add drm_ctm_to_coeffs()

[Brian Starkey]

Hi James,

On Mon, Sep 30, 2019 at 04:54:41AM +0000, james qian wang (Arm Technology China) wrote:
> This function is used to convert drm_color_ctm S31.32 sign-magnitude
> value to komeda required Q2.12 2's complement
> 
> Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@xxxxxxx>
> ---
>  .../arm/display/komeda/komeda_color_mgmt.c    | 27 +++++++++++++++++++
>  .../arm/display/komeda/komeda_color_mgmt.h    |  1 +
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c
> index c180ce70c26c..c92c82eebddb 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c
> @@ -117,3 +117,30 @@ void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs)
>  {
>  	drm_lut_to_coeffs(lut_blob, coeffs, sector_tbl, ARRAY_SIZE(sector_tbl));
>  }
> +
> +/* Convert from S31.32 sign-magnitude to HW Q2.12 2's complement */
> +static s32 drm_ctm_s31_32_to_q2_12(u64 input)
> +{
> +	u64 mag = (input & ~BIT_ULL(63)) >> 20;
> +	bool negative = !!(input & BIT_ULL(63));
> +	u32 val;
> +
> +	/* the range of signed 2s complement is [-2^n, 2^n - 1] */
> +	val = clamp_val(mag, 0, negative ? BIT(14) : BIT(14) - 1);
> +
> +	return negative ? 0 - val : val;
> +}

This function looks generally useful. Should it be in DRM core
(assuming there isn't already one there)?

You can use a parameter to determine the number of bits desired in the
output.

Thanks,
-Brian

> +
> +void drm_ctm_to_coeffs(struct drm_property_blob *ctm_blob, u32 *coeffs)
> +{
> +	struct drm_color_ctm *ctm;
> +	u32 i;
> +
> +	if (!ctm_blob)
> +		return;
> +
> +	ctm = ctm_blob->data;
> +
> +	for (i = 0; i < KOMEDA_N_CTM_COEFFS; i++)
> +		coeffs[i] = drm_ctm_s31_32_to_q2_12(ctm->matrix[i]);
> +}
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.h b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.h
> index 08ab69281648..2f4668466112 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.h
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.h
> @@ -18,6 +18,7 @@
>  #define KOMEDA_N_CTM_COEFFS		9
>  
>  void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs);
> +void drm_ctm_to_coeffs(struct drm_property_blob *ctm_blob, u32 *coeffs);
>  
>  const s32 *komeda_select_yuv2rgb_coeffs(u32 color_encoding, u32 color_range);
>  
> -- 
> 2.20.1
>