Re: [PATCH 1/2] drm/i915/dp: Fix dsc bpp calculations, v5.

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On Wed, Sep 25, 2019 at 10:21:09AM +0200, Maarten Lankhorst wrote:
> There was a integer wraparound when mode_clock became too high,
> and we didn't correct for the FEC overhead factor when dividing,
> with the calculations breaking at HBR3.
> 
> As a result our calculated bpp was way too high, and the link width
> limitation never came into effect.
> 
> Print out the resulting bpp calcululations as a sanity check, just
> in case we ever have to debug it later on again.
> 
> We also used the wrong factor for FEC. While bspec mentions 2.4%,
> all the calculations use 1/0.972261, and the same ratio should be
> applied to data M/N as well, so use it there when FEC is enabled.
> 
> This fixes the FIFO underrun we are seeing with FEC enabled.
> 
> Changes since v2:
> - Handle fec_enable in intel_link_compute_m_n, so only data M/N is adjusted. (Ville)
> - Fix initial hardware readout for FEC. (Ville)
> Changes since v3:
> - Remove bogus fec_to_mode_clock. (Ville)
> Changes since v4:
> - Use the correct register for icl. (Ville)
> - Split hw readout to a separate patch.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Fixes: d9218c8f6cf4 ("drm/i915/dp: Add helpers for Compressed BPP and Slice Count for DSC")
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.0+
> Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c |  12 +-
>  drivers/gpu/drm/i915/display/intel_display.h |   2 +-
>  drivers/gpu/drm/i915/display/intel_dp.c      | 184 ++++++++++---------
>  drivers/gpu/drm/i915/display/intel_dp.h      |   6 +-
>  drivers/gpu/drm/i915/display/intel_dp_mst.c  |   2 +-
>  5 files changed, 107 insertions(+), 99 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 5ecf54270181..c4c9286be987 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -7291,7 +7291,7 @@ static int ironlake_fdi_compute_config(struct intel_crtc *intel_crtc,
>  	pipe_config->fdi_lanes = lane;
>  
>  	intel_link_compute_m_n(pipe_config->pipe_bpp, lane, fdi_dotclock,
> -			       link_bw, &pipe_config->fdi_m_n, false);
> +			       link_bw, &pipe_config->fdi_m_n, false, false);
>  
>  	ret = ironlake_check_fdi_lanes(dev, intel_crtc->pipe, pipe_config);
>  	if (ret == -EDEADLK)
> @@ -7538,11 +7538,15 @@ void
>  intel_link_compute_m_n(u16 bits_per_pixel, int nlanes,
>  		       int pixel_clock, int link_clock,
>  		       struct intel_link_m_n *m_n,
> -		       bool constant_n)
> +		       bool constant_n, bool fec_enable)
>  {
> -	m_n->tu = 64;
> +	u32 data_clock = bits_per_pixel * pixel_clock;
> +
> +	if (fec_enable)
> +		data_clock = intel_dp_mode_to_fec_clock(data_clock);
>  
> -	compute_m_n(bits_per_pixel * pixel_clock,
> +	m_n->tu = 64;
> +	compute_m_n(data_clock,
>  		    link_clock * nlanes * 8,
>  		    &m_n->gmch_m, &m_n->gmch_n,
>  		    constant_n);
> diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
> index 5cea6f8e107a..4b9e18e5a263 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.h
> +++ b/drivers/gpu/drm/i915/display/intel_display.h
> @@ -443,7 +443,7 @@ enum phy_fia {
>  void intel_link_compute_m_n(u16 bpp, int nlanes,
>  			    int pixel_clock, int link_clock,
>  			    struct intel_link_m_n *m_n,
> -			    bool constant_n);
> +			    bool constant_n, bool fec_enable);
>  bool is_ccs_modifier(u64 modifier);
>  void lpt_disable_clkout_dp(struct drm_i915_private *dev_priv);
>  u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 829559f97440..2b1e71f992b0 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -76,8 +76,8 @@
>  #define DP_DSC_MAX_ENC_THROUGHPUT_0		340000
>  #define DP_DSC_MAX_ENC_THROUGHPUT_1		400000
>  
> -/* DP DSC FEC Overhead factor = (100 - 2.4)/100 */
> -#define DP_DSC_FEC_OVERHEAD_FACTOR		976
> +/* DP DSC FEC Overhead factor = 1/(0.972261) */
> +#define DP_DSC_FEC_OVERHEAD_FACTOR		972261
>  
>  /* Compliance test status bits  */
>  #define INTEL_DP_RESOLUTION_SHIFT_MASK	0
> @@ -492,6 +492,97 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  	return 0;
>  }
>  
> +u32 intel_dp_mode_to_fec_clock(u32 mode_clock)
> +{
> +	return div_u64(mul_u32_u32(mode_clock, 1000000U),
> +		       DP_DSC_FEC_OVERHEAD_FACTOR);
> +}
> +
> +static u16 intel_dp_dsc_get_output_bpp(u32 link_clock, u32 lane_count,
> +				       u32 mode_clock, u32 mode_hdisplay)
> +{
> +	u32 bits_per_pixel, max_bpp_small_joiner_ram;
> +	int i;
> +
> +	/*
> +	 * Available Link Bandwidth(Kbits/sec) = (NumberOfLanes)*
> +	 * (LinkSymbolClock)* 8 * (TimeSlotsPerMTP)
> +	 * for SST -> TimeSlotsPerMTP is 1,
> +	 * for MST -> TimeSlotsPerMTP has to be calculated
> +	 */
> +	bits_per_pixel = (link_clock * lane_count * 8) /
> +			 intel_dp_mode_to_fec_clock(mode_clock);

Hmm. Aren't we adding the FEC overhead twice now when DSC is also
enabled?

> +	DRM_DEBUG_KMS("Max link bpp: %u\n", bits_per_pixel);
> +
> +	/* Small Joiner Check: output bpp <= joiner RAM (bits) / Horiz. width */
> +	max_bpp_small_joiner_ram = DP_DSC_MAX_SMALL_JOINER_RAM_BUFFER / mode_hdisplay;
> +	DRM_DEBUG_KMS("Max small joiner bpp: %u\n", max_bpp_small_joiner_ram);
> +
> +	/*
> +	 * Greatest allowed DSC BPP = MIN (output BPP from available Link BW
> +	 * check, output bpp from small joiner RAM check)
> +	 */
> +	bits_per_pixel = min(bits_per_pixel, max_bpp_small_joiner_ram);
> +
> +	/* Error out if the max bpp is less than smallest allowed valid bpp */
> +	if (bits_per_pixel < valid_dsc_bpp[0]) {
> +		DRM_DEBUG_KMS("Unsupported BPP %u, min %u\n",
> +			      bits_per_pixel, valid_dsc_bpp[0]);
> +		return 0;
> +	}
> +
> +	/* Find the nearest match in the array of known BPPs from VESA */
> +	for (i = 0; i < ARRAY_SIZE(valid_dsc_bpp) - 1; i++) {
> +		if (bits_per_pixel < valid_dsc_bpp[i + 1])
> +			break;
> +	}
> +	bits_per_pixel = valid_dsc_bpp[i];
> +
> +	/*
> +	 * Compressed BPP in U6.4 format so multiply by 16, for Gen 11,
> +	 * fractional part is 0
> +	 */
> +	return bits_per_pixel << 4;
> +}
> +
> +static u8 intel_dp_dsc_get_slice_count(struct intel_dp *intel_dp,
> +				       int mode_clock, int mode_hdisplay)
> +{
> +	u8 min_slice_count, i;
> +	int max_slice_width;
> +
> +	if (mode_clock <= DP_DSC_PEAK_PIXEL_RATE)
> +		min_slice_count = DIV_ROUND_UP(mode_clock,
> +					       DP_DSC_MAX_ENC_THROUGHPUT_0);
> +	else
> +		min_slice_count = DIV_ROUND_UP(mode_clock,
> +					       DP_DSC_MAX_ENC_THROUGHPUT_1);
> +
> +	max_slice_width = drm_dp_dsc_sink_max_slice_width(intel_dp->dsc_dpcd);
> +	if (max_slice_width < DP_DSC_MIN_SLICE_WIDTH_VALUE) {
> +		DRM_DEBUG_KMS("Unsupported slice width %d by DP DSC Sink device\n",
> +			      max_slice_width);
> +		return 0;
> +	}
> +	/* Also take into account max slice width */
> +	min_slice_count = min_t(u8, min_slice_count,
> +				DIV_ROUND_UP(mode_hdisplay,
> +					     max_slice_width));
> +
> +	/* Find the closest match to the valid slice count values */
> +	for (i = 0; i < ARRAY_SIZE(valid_dsc_slicecount); i++) {
> +		if (valid_dsc_slicecount[i] >
> +		    drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
> +						    false))
> +			break;
> +		if (min_slice_count  <= valid_dsc_slicecount[i])
> +			return valid_dsc_slicecount[i];
> +	}
> +
> +	DRM_DEBUG_KMS("Unsupported Slice Count %d\n", min_slice_count);
> +	return 0;
> +}
> +
>  static enum drm_mode_status
>  intel_dp_mode_valid(struct drm_connector *connector,
>  		    struct drm_display_mode *mode)
> @@ -2259,7 +2350,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       pipe_config->port_clock,
>  			       &pipe_config->dp_m_n,
> -			       constant_n);
> +			       constant_n, pipe_config->fec_enable);
>  
>  	if (intel_connector->panel.downclock_mode != NULL &&
>  		dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) {
> @@ -2269,7 +2360,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  					       intel_connector->panel.downclock_mode->clock,
>  					       pipe_config->port_clock,
>  					       &pipe_config->dp_m2_n2,
> -					       constant_n);
> +					       constant_n, pipe_config->fec_enable);
>  	}
>  
>  	if (!HAS_DDI(dev_priv))
> @@ -4373,91 +4464,6 @@ intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *sink_irq_vector)
>  		DP_DPRX_ESI_LEN;
>  }
>  
> -u16 intel_dp_dsc_get_output_bpp(int link_clock, u8 lane_count,
> -				int mode_clock, int mode_hdisplay)
> -{
> -	u16 bits_per_pixel, max_bpp_small_joiner_ram;
> -	int i;
> -
> -	/*
> -	 * Available Link Bandwidth(Kbits/sec) = (NumberOfLanes)*
> -	 * (LinkSymbolClock)* 8 * ((100-FECOverhead)/100)*(TimeSlotsPerMTP)
> -	 * FECOverhead = 2.4%, for SST -> TimeSlotsPerMTP is 1,
> -	 * for MST -> TimeSlotsPerMTP has to be calculated
> -	 */
> -	bits_per_pixel = (link_clock * lane_count * 8 *
> -			  DP_DSC_FEC_OVERHEAD_FACTOR) /
> -		mode_clock;
> -
> -	/* Small Joiner Check: output bpp <= joiner RAM (bits) / Horiz. width */
> -	max_bpp_small_joiner_ram = DP_DSC_MAX_SMALL_JOINER_RAM_BUFFER /
> -		mode_hdisplay;
> -
> -	/*
> -	 * Greatest allowed DSC BPP = MIN (output BPP from avaialble Link BW
> -	 * check, output bpp from small joiner RAM check)
> -	 */
> -	bits_per_pixel = min(bits_per_pixel, max_bpp_small_joiner_ram);
> -
> -	/* Error out if the max bpp is less than smallest allowed valid bpp */
> -	if (bits_per_pixel < valid_dsc_bpp[0]) {
> -		DRM_DEBUG_KMS("Unsupported BPP %d\n", bits_per_pixel);
> -		return 0;
> -	}
> -
> -	/* Find the nearest match in the array of known BPPs from VESA */
> -	for (i = 0; i < ARRAY_SIZE(valid_dsc_bpp) - 1; i++) {
> -		if (bits_per_pixel < valid_dsc_bpp[i + 1])
> -			break;
> -	}
> -	bits_per_pixel = valid_dsc_bpp[i];
> -
> -	/*
> -	 * Compressed BPP in U6.4 format so multiply by 16, for Gen 11,
> -	 * fractional part is 0
> -	 */
> -	return bits_per_pixel << 4;
> -}
> -
> -u8 intel_dp_dsc_get_slice_count(struct intel_dp *intel_dp,
> -				int mode_clock,
> -				int mode_hdisplay)
> -{
> -	u8 min_slice_count, i;
> -	int max_slice_width;
> -
> -	if (mode_clock <= DP_DSC_PEAK_PIXEL_RATE)
> -		min_slice_count = DIV_ROUND_UP(mode_clock,
> -					       DP_DSC_MAX_ENC_THROUGHPUT_0);
> -	else
> -		min_slice_count = DIV_ROUND_UP(mode_clock,
> -					       DP_DSC_MAX_ENC_THROUGHPUT_1);
> -
> -	max_slice_width = drm_dp_dsc_sink_max_slice_width(intel_dp->dsc_dpcd);
> -	if (max_slice_width < DP_DSC_MIN_SLICE_WIDTH_VALUE) {
> -		DRM_DEBUG_KMS("Unsupported slice width %d by DP DSC Sink device\n",
> -			      max_slice_width);
> -		return 0;
> -	}
> -	/* Also take into account max slice width */
> -	min_slice_count = min_t(u8, min_slice_count,
> -				DIV_ROUND_UP(mode_hdisplay,
> -					     max_slice_width));
> -
> -	/* Find the closest match to the valid slice count values */
> -	for (i = 0; i < ARRAY_SIZE(valid_dsc_slicecount); i++) {
> -		if (valid_dsc_slicecount[i] >
> -		    drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
> -						    false))
> -			break;
> -		if (min_slice_count  <= valid_dsc_slicecount[i])
> -			return valid_dsc_slicecount[i];
> -	}
> -
> -	DRM_DEBUG_KMS("Unsupported Slice Count %d\n", min_slice_count);
> -	return 0;
> -}
> -
>  static void
>  intel_pixel_encoding_setup_vsc(struct intel_dp *intel_dp,
>  			       const struct intel_crtc_state *crtc_state)
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index e01d1f89409d..a194b5b6da05 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -103,10 +103,6 @@ bool intel_dp_source_supports_hbr2(struct intel_dp *intel_dp);
>  bool intel_dp_source_supports_hbr3(struct intel_dp *intel_dp);
>  bool
>  intel_dp_get_link_status(struct intel_dp *intel_dp, u8 *link_status);
> -u16 intel_dp_dsc_get_output_bpp(int link_clock, u8 lane_count,
> -				int mode_clock, int mode_hdisplay);
> -u8 intel_dp_dsc_get_slice_count(struct intel_dp *intel_dp, int mode_clock,
> -				int mode_hdisplay);
>  
>  bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
>  bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp);
> @@ -119,4 +115,6 @@ static inline unsigned int intel_dp_unused_lane_mask(int lane_count)
>  	return ~((1 << lane_count) - 1) & 0xf;
>  }
>  
> +u32 intel_dp_mode_to_fec_clock(u32 mode_clock);
> +
>  #endif /* __INTEL_DP_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index eeeb3f933aa4..cf4d851a5139 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -81,7 +81,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       crtc_state->port_clock,
>  			       &crtc_state->dp_m_n,
> -			       constant_n);
> +			       constant_n, crtc_state->fec_enable);
>  	crtc_state->dp_m_n.tu = slots;
>  
>  	return 0;
> -- 
> 2.20.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel
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