Re: [PATCH 10/10] drm/i915: Skip the linear degamma LUT load on ICL+

[Matt Roper <matthew.d.roper@intel.com>]

On Mon, Mar 18, 2019 at 06:13:17PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Don't load the linear degamma LUT on ICL. The hardware no longer
> has any silly linkages between the CSC enable and degamma LUT
> enable so the degamma LUT is only needed when it's actually
> enabled.
> 
> Also add comments to explain the situation on GLK.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_color.c | 89 +++++++++++++++++++++---------
>  1 file changed, 63 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_color.c b/drivers/gpu/drm/i915/intel_color.c
> index b84a2a3f5844..95e44f80bd8a 100644
> --- a/drivers/gpu/drm/i915/intel_color.c
> +++ b/drivers/gpu/drm/i915/intel_color.c
> @@ -273,6 +273,14 @@ static void ilk_load_csc_matrix(const struct intel_crtc_state *crtc_state)
>  				    ilk_csc_coeff_limited_range,
>  				    ilk_csc_postoff_limited_range);
>  	} else if (crtc_state->csc_enable) {
> +		/*
> +		 * On GLK+ both pipe CSC and degamma LUT are controlled
> +		 * by csc_enable. Hence for the cases where the degama
> +		 * LUT is needed but CSC is not we need to load an
> +		 * identity matrix.
> +		 */
> +		WARN_ON(!IS_CANNONLAKE(dev_priv) && !IS_GEMINILAKE(dev_priv));
> +
>  		ilk_update_pipe_csc(crtc, ilk_csc_off_zero,
>  				    ilk_csc_coeff_identity,
>  				    ilk_csc_off_zero);
> @@ -559,6 +567,7 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
>  	enum pipe pipe = crtc->pipe;
>  	const u32 lut_size = INTEL_INFO(dev_priv)->color.degamma_lut_size;
> +	struct drm_color_lut *lut = crtc_state->base.degamma_lut->data;
>  	u32 i;
>  
>  	/*
> @@ -569,32 +578,48 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
>  	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), 0);
>  	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), PRE_CSC_GAMC_AUTO_INCREMENT);
>  
> -	if (crtc_state->base.degamma_lut) {
> -		struct drm_color_lut *lut = crtc_state->base.degamma_lut->data;
> +	for (i = 0; i < lut_size; i++) {
> +		/*
> +		 * First 33 entries represent range from 0 to 1.0
> +		 * 34th and 35th entry will represent extended range
> +		 * inputs 3.0 and 7.0 respectively, currently clamped
> +		 * at 1.0. Since the precision is 16bit, the user
> +		 * value can be directly filled to register.
> +		 * The pipe degamma table in GLK+ onwards doesn't
> +		 * support different values per channel, so this just
> +		 * programs green value which will be equal to Red and
> +		 * Blue into the lut registers.
> +		 * ToDo: Extend to max 7.0. Enable 32 bit input value
> +		 * as compared to just 16 to achieve this.
> +		 */
> +		I915_WRITE(PRE_CSC_GAMC_DATA(pipe), lut[i].green);
> +	}
>  
> -		for (i = 0; i < lut_size; i++) {
> -			/*
> -			 * First 33 entries represent range from 0 to 1.0
> -			 * 34th and 35th entry will represent extended range
> -			 * inputs 3.0 and 7.0 respectively, currently clamped
> -			 * at 1.0. Since the precision is 16bit, the user
> -			 * value can be directly filled to register.
> -			 * The pipe degamma table in GLK+ onwards doesn't
> -			 * support different values per channel, so this just
> -			 * programs green value which will be equal to Red and
> -			 * Blue into the lut registers.
> -			 * ToDo: Extend to max 7.0. Enable 32 bit input value
> -			 * as compared to just 16 to achieve this.
> -			 */
> -			I915_WRITE(PRE_CSC_GAMC_DATA(pipe), lut[i].green);
> -		}
> -	} else {
> -		/* load a linear table. */
> -		for (i = 0; i < lut_size; i++) {
> -			u32 v = (i * (1 << 16)) / (lut_size - 1);
> +	/* Clamp values > 1.0. */
> +	while (i++ < 35)
> +		I915_WRITE(PRE_CSC_GAMC_DATA(pipe), (1 << 16));
> +}
>  
> -			I915_WRITE(PRE_CSC_GAMC_DATA(pipe), v);
> -		}
> +static void glk_load_degamma_lut_linear(const struct intel_crtc_state *crtc_state)
> +{
> +	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
> +	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> +	enum pipe pipe = crtc->pipe;
> +	const u32 lut_size = INTEL_INFO(dev_priv)->color.degamma_lut_size;
> +	u32 i;
> +
> +	/*
> +	 * When setting the auto-increment bit, the hardware seems to
> +	 * ignore the index bits, so we need to reset it to index 0
> +	 * separately.
> +	 */
> +	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), 0);
> +	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), PRE_CSC_GAMC_AUTO_INCREMENT);
> +
> +	for (i = 0; i < lut_size; i++) {
> +		u32 v = (i  << 16) / (lut_size - 1);
> +
> +		I915_WRITE(PRE_CSC_GAMC_DATA(pipe), v);
>  	}
>  
>  	/* Clamp values > 1.0. */
> @@ -604,7 +629,18 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
>  
>  static void glk_load_luts(const struct intel_crtc_state *crtc_state)
>  {
> -	glk_load_degamma_lut(crtc_state);
> +	/*
> +	 * On GLK+ both pipe CSC and degamma LUT are controlled
> +	 * by csc_enable. Hence for the cases where the CSC is
> +	 * needed but degamma LUT is not we need to load a
> +	 * linear degamma LUT. In fact we'll just always load
> +	 * the degama LUT so that we don't have to reload
> +	 * it every time the pipe CSC is being enabled.
> +	 */
> +	if (crtc_state->base.degamma_lut)
> +		glk_load_degamma_lut(crtc_state);
> +	else
> +		glk_load_degamma_lut_linear(crtc_state);
>  
>  	if (crtc_state_is_legacy_gamma(crtc_state))
>  		i9xx_load_luts(crtc_state);
> @@ -614,7 +650,8 @@ static void glk_load_luts(const struct intel_crtc_state *crtc_state)
>  
>  static void icl_load_luts(const struct intel_crtc_state *crtc_state)
>  {
> -	glk_load_degamma_lut(crtc_state);
> +	if (crtc_state->base.degamma_lut)
> +		glk_load_degamma_lut(crtc_state);
>  
>  	if (crtc_state_is_legacy_gamma(crtc_state))
>  		i9xx_load_luts(crtc_state);
> -- 
> 2.19.2
> 

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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