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
