[Intel-gfx] [PATCH 5/8] drm/i915/dsc/mtl: Add support for fractional bpp

[Kandpal, Suraj]

> Subject: [PATCH 5/8] drm/i915/dsc/mtl: Add support for fractional bpp
> 
> From: Vandita Kulkarni <vandita.kulkarni at intel.com>
> 
> Consider the fractional bpp while reading the qp values.
> 
> v2: Use helpers for fractional, integral bits of bits_per_pixel. (Suraj)
> 

LGTM.
Reviewed-by: Suraj Kandpal <suraj.kandpal at intel.com>

> Signed-off-by: Vandita Kulkarni <vandita.kulkarni at intel.com>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> ---
>  .../gpu/drm/i915/display/intel_qp_tables.c    |  3 ---
>  drivers/gpu/drm/i915/display/intel_vdsc.c     | 25 +++++++++++++++----
>  2 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_qp_tables.c
> b/drivers/gpu/drm/i915/display/intel_qp_tables.c
> index 543cdc46aa1d..600c815e37e4 100644
> --- a/drivers/gpu/drm/i915/display/intel_qp_tables.c
> +++ b/drivers/gpu/drm/i915/display/intel_qp_tables.c
> @@ -34,9 +34,6 @@
>   * These qp tables are as per the C model
>   * and it has the rows pointing to bpps which increment
>   * in steps of 0.5
> - * We do not support fractional bpps as of today,
> - * hence we would skip the fractional bpps during
> - * our references for qp calclulations.
>   */
>  static const u8
> rc_range_minqp444_8bpc[DSC_NUM_BUF_RANGES][RC_RANGE_QP444_8BPC
> _MAX_NUM_BPP] = {
>  	{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, diff --git
> a/drivers/gpu/drm/i915/display/intel_vdsc.c
> b/drivers/gpu/drm/i915/display/intel_vdsc.c
> index bfc41972a0bb..d7cfb2446c13 100644
> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
> @@ -77,8 +77,8 @@ intel_vdsc_set_min_max_qp(struct drm_dsc_config
> *vdsc_cfg, int buf,  static void  calculate_rc_params(struct drm_dsc_config
> *vdsc_cfg)  {
> +	int bpp = to_bpp_int(vdsc_cfg->bits_per_pixel);
>  	int bpc = vdsc_cfg->bits_per_component;
> -	int bpp = vdsc_cfg->bits_per_pixel >> 4;
>  	int qp_bpc_modifier = (bpc - 8) * 2;
>  	int uncompressed_bpg_rate;
>  	int first_line_bpg_offset;
> @@ -148,7 +148,13 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
>  		static const s8 ofs_und8[] = {
>  			10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -10, -12, -12, -12
>  		};
> -
> +		/*
> +		 * For 420 format since bits_per_pixel (bpp) is set to target bpp
> * 2,
> +		 * QP table values for target bpp 4.0 to 4.4375 (rounded to 4.0)
> are
> +		 * actually for bpp 8 to 8.875 (rounded to 4.0 * 2 i.e 8).
> +		 * Similarly values for target bpp 4.5 to 4.8375 (rounded to 4.5)
> +		 * are for bpp 9 to 9.875 (rounded to 4.5 * 2 i.e 9), and so on.
> +		 */
>  		bpp_i  = bpp - 8;
>  		for (buf_i = 0; buf_i < DSC_NUM_BUF_RANGES; buf_i++) {
>  			u8 range_bpg_offset;
> @@ -178,6 +184,9 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
>  				range_bpg_offset &
> DSC_RANGE_BPG_OFFSET_MASK;
>  		}
>  	} else {
> +		/* fractional bpp part * 10000 (for precision up to 4 decimal
> places) */
> +		int fractional_bits = to_bpp_frac_dec(vdsc_cfg-
> >bits_per_pixel);
> +
>  		static const s8 ofs_und6[] = {
>  			0, -2, -2, -4, -6, -6, -8, -8, -8, -10, -10, -12, -12, -12, -12
>  		};
> @@ -191,7 +200,14 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
>  			10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -10, -12, -12, -12
>  		};
> 
> -		bpp_i  = (2 * (bpp - 6));
> +		/*
> +		 * QP table rows have values in increment of 0.5.
> +		 * So 6.0 bpp to 6.4375 will have index 0, 6.5 to 6.9375 will
> have index 1,
> +		 * and so on.
> +		 * 0.5 fractional part with 4 decimal precision becomes 5000
> +		 */
> +		bpp_i  = ((bpp - 6) + (fractional_bits < 5000 ? 0 : 1));
> +
>  		for (buf_i = 0; buf_i < DSC_NUM_BUF_RANGES; buf_i++) {
>  			u8 range_bpg_offset;
> 
> @@ -279,8 +295,7 @@ int intel_dsc_compute_params(struct intel_crtc_state
> *pipe_config)
>  	/* Gen 11 does not support VBR */
>  	vdsc_cfg->vbr_enable = false;
> 
> -	/* Gen 11 only supports integral values of bpp */
> -	vdsc_cfg->bits_per_pixel = compressed_bpp << 4;
> +	vdsc_cfg->bits_per_pixel = pipe_config->dsc.compressed_bpp_x16;
> 
>  	/*
>  	 * According to DSC 1.2 specs in Section 4.1 if native_420 is set
> --
> 2.25.1