Re: [PATCH v2 1/4] drm/komeda: Add a new helper drm_color_ctm_s31_32_to_qm_n()

[Daniel Vetter]

On Fri, Oct 11, 2019 at 05:43:09AM +0000, james qian wang (Arm Technology China) wrote:
> Add a new helper function drm_color_ctm_s31_32_to_qm_n() for driver to
> convert S31.32 sign-magnitude to Qm.n 2's complement that supported by
> hardware.
> 
> Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@xxxxxxx>
> ---
>  drivers/gpu/drm/drm_color_mgmt.c | 23 +++++++++++++++++++++++
>  include/drm/drm_color_mgmt.h     |  2 ++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> index 4ce5c6d8de99..3d533d0b45af 100644
> --- a/drivers/gpu/drm/drm_color_mgmt.c
> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> @@ -132,6 +132,29 @@ uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)
>  }
>  EXPORT_SYMBOL(drm_color_lut_extract);
>  
> +/**
> + * drm_color_ctm_s31_32_to_qm_n
> + *
> + * @user_input: input value
> + * @m: number of integer bits
> + * @n: number of fractinal bits
> + *
> + * Convert and clamp S31.32 sign-magnitude to Qm.n 2's complement.

What's the Q meaning here? Also maybe specify that the higher bits above
m+n are cleared to all 0 or all 1. Unit test would be lovely too. Anyway:

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

> + */
> +uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
> +				      uint32_t m, uint32_t n)
> +{
> +	u64 mag = (user_input & ~BIT_ULL(63)) >> (32 - n);
> +	bool negative = !!(user_input & BIT_ULL(63));
> +	s64 val;
> +
> +	/* the range of signed 2s complement is [-2^n+m, 2^n+m - 1] */
> +	val = clamp_val(mag, 0, negative ? BIT(n + m) : BIT(n + m) - 1);
> +
> +	return negative ? 0ll - val : val;
> +}
> +EXPORT_SYMBOL(drm_color_ctm_s31_32_to_qm_n);
> +
>  /**
>   * drm_crtc_enable_color_mgmt - enable color management properties
>   * @crtc: DRM CRTC
> diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
> index d1c662d92ab7..60fea5501886 100644
> --- a/include/drm/drm_color_mgmt.h
> +++ b/include/drm/drm_color_mgmt.h
> @@ -30,6 +30,8 @@ struct drm_crtc;
>  struct drm_plane;
>  
>  uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
> +uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
> +				      uint32_t m, uint32_t n);
>  
>  void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
>  				uint degamma_lut_size,
> -- 
> 2.20.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch