Re: [v6 01/16] drm: Add Enhanced Gamma LUT precision structure

["Lankhorst, Maarten" <maarten.lankhorst@intel.com>]

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tis 2019-03-19 klockan 14:14 +0530 skrev Uma Shankar:
> Existing LUT precision structure is having only 16 bit
> precision. This is not enough for upcoming enhanced hardwares
> and advance usecases like HDR processing. Hence added a new
> structure with 32 bit precision values. Also added the code,
> for extracting the same from values passed from userspace.
> 
> v4: Rebase
> 
> v5: Relocated the helper function to drm_color_mgmt.c. Declared
> the same in a header file (Alexandru Gheorghe)
> 
> v6: Enhanced gamma lut structure to take U32.32 format as input.
> This is needed for HDR usecase which require higher precision.
> 
> Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> Reviewed-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
> ---
>  drivers/gpu/drm/drm_color_mgmt.c | 19 +++++++++++++++++++
>  include/drm/drm_color_mgmt.h     |  1 +
>  include/uapi/drm/drm_mode.h      | 15 +++++++++++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_color_mgmt.c
> b/drivers/gpu/drm/drm_color_mgmt.c
> index d5d34d0..9dbfe1d 100644
> --- a/drivers/gpu/drm/drm_color_mgmt.c
> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> @@ -128,6 +128,25 @@ uint32_t drm_color_lut_extract(uint32_t
> user_input, uint32_t bit_precision)
>  }
>  EXPORT_SYMBOL(drm_color_lut_extract);
>  
> +/*
> + * Added to accommodate enhanced LUT precision.
> + * Max LUT precision is 32 bits.
> + */
> +u64 drm_color_lut_extract_ext(u64 user_input, u32 bit_precision)
> +{
> +	u32 val = user_input & 0xffffffff;
> +	u32 max = 0xffffffff >> (32 - bit_precision);
> +
> +	/* Round only if we're not using full precision. */
> +	if (bit_precision < 32) {
> +		val += 1UL << (32 - bit_precision - 1);
> +		val >>= 32 - bit_precision;
> +	}
> +
> +	return ((user_input & 0xffffffff) | clamp_val(val, 0, max));
I thought the userspace precision was U32.32, so the precision here is
max 64-bits?

Anyway the math looks wrong for a U32.32 value, it's probably:
user_input >> (64ULL - precision)

> +}
> +EXPORT_SYMBOL(drm_color_lut_extract_ext);
> +
>  /**
>   * 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 d1c662d..c9d2746 100644
> --- a/include/drm/drm_color_mgmt.h
> +++ b/include/drm/drm_color_mgmt.h
> @@ -30,6 +30,7 @@
>  struct drm_plane;
>  
>  uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t
> bit_precision);
> +u64 drm_color_lut_extract_ext(u64 user_input, u32 bit_precision);
>  
>  void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
>  				uint degamma_lut_size,
> diff --git a/include/uapi/drm/drm_mode.h
> b/include/uapi/drm/drm_mode.h
> index a439c2e..a0fae71 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -630,6 +630,21 @@ struct drm_color_lut {
>  	__u16 reserved;
>  };
>  
> +/*
> + * Creating 64 bit palette entries for better data
> + * precision. This will be required for HDR and
> + * similar color processing usecases.
> + */
> +struct drm_color_lut_ext {
> +	/*
> +	 * Data is U32.32 fixed point format.
> +	 */
> +	__u64 red;
> +	__u64 green;
> +	__u64 blue;
> +	__u64 reserved;
> +};
> +
>  #define DRM_MODE_PAGE_FLIP_EVENT 0x01
>  #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
>  #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4

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