Re: [PATCH v2 4/5] drm/i915/display: Add Nearest-neighbor based integer scaling support

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Mar 19, 2020 at 03:51:02PM +0530, Pankaj Bharadiya wrote:
> Integer scaling (IS) is a nearest-neighbor upscaling technique that
> simply scales up the existing pixels by an integer
> (i.e., whole number) multiplier.Nearest-neighbor (NN) interpolation
> works by filling in the missing color values in the upscaled image
> with that of the coordinate-mapped nearest source pixel value.
> 
> Both IS and NN preserve the clarity of the original image. Integer
> scaling is particularly useful for pixel art games that rely on
> sharp, blocky images to deliver their distinctive look.
> 
> Introduce skl_scaler_setup_nearest_neighbor_filter() function which
> configures the scaler filter coefficients to enable nearest-neighbor
> filtering.
> 
> Bspec: 49247
> 
> changes since v1:
> * Rearrange skl_scaler_setup_nearest_neighbor_filter() to iterate the
>   registers directly instead of the phases and taps (Ville)
> 
> changes since RFC:
> * Refine the skl_scaler_setup_nearest_neighbor_filter() logic (Ville)
> 
> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 72 ++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_display.h |  2 +
>  2 files changed, 74 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 8f23c4d51c33..791dd908aa89 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -6237,6 +6237,78 @@ void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state)
>  		skl_detach_scaler(crtc, i);
>  }
>  
> +static int skl_coef_tap(int i)
> +{
> +	return i % 7;
> +}
> +
> +static u16 skl_nearest_filter_coef(int t)
> +{
> +	return t == 3 ? 0x0800 : 0x3000;
> +}
> +
> +/**
> + *  Theory behind setting nearest-neighbor integer scaling:
> + *
> + *  17 phase of 7 taps requires 119 coefficients in 60 dwords per set.
> + *  The letter represents the filter tap (D is the center tap) and the number
> + *  represents the coefficient set for a phase (0-16).
> + *
> + *         +------------+------------------------+------------------------+
> + *         |Index value | Data value coeffient 1 | Data value coeffient 2 |
> + *         +------------+------------------------+------------------------+
> + *         |   00h      |          B0            |          A0            |
> + *         +------------+------------------------+------------------------+
> + *         |   01h      |          D0            |          C0            |
> + *         +------------+------------------------+------------------------+
> + *         |   02h      |          F0            |          E0            |
> + *         +------------+------------------------+------------------------+
> + *         |   03h      |          A1            |          G0            |
> + *         +------------+------------------------+------------------------+
> + *         |   04h      |          C1            |          B1            |
> + *         +------------+------------------------+------------------------+
> + *         |   ...      |          ...           |          ...           |
> + *         +------------+------------------------+------------------------+
> + *         |   38h      |          B16           |          A16           |
> + *         +------------+------------------------+------------------------+
> + *         |   39h      |          D16           |          C16           |
> + *         +------------+------------------------+------------------------+
> + *         |   3Ah      |          F16           |          C16           |
> + *         +------------+------------------------+------------------------+
> + *         |   3Bh      |        Reserved        |          G16           |
> + *         +------------+------------------------+------------------------+
> + *
> + *  To enable nearest-neighbor scaling:  program scaler coefficents with
> + *  the center tap (Dxx) values set to 1 and all other values set to 0 as per
> + *  SCALER_COEFFICIENT_FORMAT
> + *
> + */
> +
> +void skl_scaler_setup_nearest_neighbor_filter(struct drm_i915_private *dev_priv,
> +					      enum pipe pipe, int id, int set)
> +{
> +	int i;
> +
> +	/*enable the index auto increment.*/

Pointless comment, and also misformatted.

> +	intel_de_write_fw(dev_priv,
> +			  SKL_PS_COEF_INDEX_SET(pipe, id, set),
> +			  PS_COEE_INDEX_AUTO_INC);
> +
> +	for (i = 0; i < 17 * 7; i += 2) {
> +		u32 tmp;
> +		int t;
> +
> +		t = skl_coef_tap(i);
> +		tmp = skl_nearest_filter_coef(t);
> +
> +		t = skl_coef_tap(i+1);
> +		tmp |= skl_nearest_filter_coef(t)<<16;

Missing spaces.

> +
> +		intel_de_write_fw(dev_priv, SKL_PS_COEF_DATA_SET(pipe, id, set),
> +				  tmp);
> +	}

I'd maybe reset the index back to 0 here and disable the auto-increment
bit.

> +}
> +
>  static void skl_pfit_enable(const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
> index adb1225a3480..88f3c77f6806 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.h
> +++ b/drivers/gpu/drm/i915/display/intel_display.h
> @@ -587,6 +587,8 @@ void intel_crtc_arm_fifo_underrun(struct intel_crtc *crtc,
>  u16 skl_scaler_calc_phase(int sub, int scale, bool chroma_center);
>  int skl_update_scaler_crtc(struct intel_crtc_state *crtc_state);
>  void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state);
> +void skl_scaler_setup_nearest_neighbor_filter(struct drm_i915_private *dev_priv,
> +					      enum pipe pipe, int id, int set);
>  void ilk_pfit_disable(const struct intel_crtc_state *old_crtc_state);
>  u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
>  			const struct intel_plane_state *plane_state);
> -- 
> 2.23.0

-- 
Ville Syrjälä
Intel
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