On Mon, Oct 30, 2023 at 05:58:26PM +0200, Imre Deak wrote:
> Atm, the BW allocated for an MST stream doesn't take into account the
> DSC control symbol (EOC) and data alignment overhead on the local (first
> downstream) MST link (reflected by the data M/N/TU values) and - besides
> the above overheads - the FEC symbol overhead on 8b/10b remote
> (after a downstream branch device) MST links.
>
> In addition the FEC overhead used on the local link is a fixed amount,
> which only applies to certain modes, but not enough for all modes; add a
> code comment clarifying this.
>
> Fix the above by calculating the data M/N values with the total BW
> overhead (not including the SSC overhead, since this isn't enabled by
> the source device) and using this the PBN and TU values for the local
> link and PBN for remote links (including SSC, since this is mandatory
> for links after downstream branch devices).
>
> For now keep the current fixed FEC overhead as a minimum, since this is
> what bspec requires for audio functionality.
>
> Calculate the effective link BW in a clearer way, applying the channel
> coding efficiency based on the coding type. The calculation was correct
> for 8b/10b, but not for 128b/132b links; this patch leaves the behavior
> for this unchanged, leaving the fix for a follow-up.
>
> v2:
> - Fix TU size programmed to the HW, making it match the payload size
> programmed to the payload table.
>
> Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> (v1)
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_dp_mst.c | 107 +++++++++++++++-----
> 1 file changed, 82 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index dcbc5d3aa7bc3..05b2d5d547c85 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -66,6 +66,63 @@ static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp
> return 0;
> }
>
> +static int intel_dp_mst_bw_overhead(const struct intel_crtc_state *crtc_state,
> + const struct intel_connector *connector,
> + bool ssc, bool dsc, int bpp)
> +{
> + const struct drm_display_mode *adjusted_mode =
> + &crtc_state->hw.adjusted_mode;
> + unsigned long flags = DRM_DP_BW_OVERHEAD_MST;
> + int dsc_slice_count = 0;
> + int overhead;
> +
> + flags |= intel_dp_is_uhbr(crtc_state) ? DRM_DP_BW_OVERHEAD_UHBR : 0;
> + flags |= ssc ? DRM_DP_BW_OVERHEAD_SSC_REF_CLK : 0;
> + flags |= crtc_state->fec_enable ? DRM_DP_BW_OVERHEAD_FEC : 0;
> +
> + if (dsc) {
> + flags |= DRM_DP_BW_OVERHEAD_DSC;
> + /* TODO: add support for bigjoiner */
> + dsc_slice_count = intel_dp_dsc_get_slice_count(connector,
> + adjusted_mode->clock,
> + adjusted_mode->hdisplay,
> + false);
> + }
> +
> + overhead = drm_dp_bw_overhead(crtc_state->lane_count,
> + adjusted_mode->hdisplay,
> + dsc_slice_count,
> + to_bpp_x16(bpp),
> + flags);
> +
> + /*
> + * TODO: clarify whether a minimum required by the fixed FEC overhead
> + * in the bspec audio programming sequence is required here.
> + */
> + return max(overhead, intel_dp_bw_fec_overhead(crtc_state->fec_enable));
> +}
> +
> +static void intel_dp_mst_compute_m_n(const struct intel_crtc_state *crtc_state,
> + const struct intel_connector *connector,
> + bool ssc, bool dsc,
> + int bpp,
> + struct intel_link_m_n *m_n)
> +{
> + const struct drm_display_mode *adjusted_mode =
> + &crtc_state->hw.adjusted_mode;
> + int overhead = intel_dp_mst_bw_overhead(crtc_state,
> + connector,
> + ssc, dsc, bpp);
> +
> + intel_link_compute_m_n(bpp, crtc_state->lane_count,
> + adjusted_mode->crtc_clock,
> + crtc_state->port_clock,
> + overhead,
> + m_n);
> +
> + m_n->tu = DIV_ROUND_UP_ULL(mul_u32_u32(m_n->data_m, 64), m_n->data_n);
> +}
> +
> static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
> struct intel_crtc_state *crtc_state,
> int max_bpp,
> @@ -106,14 +163,34 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
> crtc_state->lane_count);
>
> for (bpp = max_bpp; bpp >= min_bpp; bpp -= step) {
> + struct intel_link_m_n remote_m_n;
> + int link_bpp;
> +
> drm_dbg_kms(&i915->drm, "Trying bpp %d\n", bpp);
>
> ret = intel_dp_mst_check_constraints(i915, bpp, adjusted_mode, crtc_state, dsc);
> if (ret)
> continue;
>
> - crtc_state->pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock,
> - bpp << 4);
> + link_bpp = dsc ? bpp :
> + intel_dp_output_bpp(crtc_state->output_format, bpp);
> +
> + intel_dp_mst_compute_m_n(crtc_state, connector, false, dsc, link_bpp,
> + &crtc_state->dp_m_n);
> + intel_dp_mst_compute_m_n(crtc_state, connector, true, dsc, link_bpp,
> + &remote_m_n);
> +
> + /*
> + * The TU size programmed to the HW determines which slots in
> + * an MTP frame are used for this stream, which needs to match
> + * the payload size programmed to the first downstream branch
> + * device's payload table.
> + */
> + crtc_state->dp_m_n.tu = remote_m_n.tu;
The fact we use the "remote" value here is because the mst manager code
assumes the two numbers are the same, right? Should perhaps highlight
that fact a bit better.
Maybe we want a WARN_ON(remote_m_n.tu < dp_m_n.tu) here as well?
> +
> + crtc_state->pbn = DIV_ROUND_UP_ULL(mul_u32_u32(mst_state->pbn_div * 64,
> + remote_m_n.data_m),
> + remote_m_n.data_n);
>
> slots = drm_dp_atomic_find_time_slots(state, &intel_dp->mst_mgr,
> connector->port,
> @@ -122,6 +199,8 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
> return slots;
>
> if (slots >= 0) {
> + drm_WARN_ON(&i915->drm, slots != remote_m_n.tu);
> +
> ret = drm_dp_mst_atomic_check(state);
> /*
> * If we got slots >= 0 and we can fit those based on check
> @@ -155,10 +234,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
> struct drm_connector_state *conn_state,
> struct link_config_limits *limits)
> {
> - const struct drm_display_mode *adjusted_mode =
> - &crtc_state->hw.adjusted_mode;
> int slots = -EINVAL;
> - int link_bpp;
>
> /*
> * FIXME: allocate the BW according to link_bpp, which in the case of
> @@ -173,16 +249,6 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
> if (slots < 0)
> return slots;
>
> - link_bpp = intel_dp_output_bpp(crtc_state->output_format, crtc_state->pipe_bpp);
> -
> - intel_link_compute_m_n(link_bpp,
> - crtc_state->lane_count,
> - adjusted_mode->crtc_clock,
> - crtc_state->port_clock,
> - intel_dp_bw_fec_overhead(crtc_state->fec_enable),
> - &crtc_state->dp_m_n);
> - crtc_state->dp_m_n.tu = slots;
> -
> return 0;
> }
>
> @@ -194,8 +260,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> struct intel_connector *connector =
> to_intel_connector(conn_state->connector);
> struct drm_i915_private *i915 = to_i915(connector->base.dev);
> - const struct drm_display_mode *adjusted_mode =
> - &crtc_state->hw.adjusted_mode;
> int slots = -EINVAL;
> int i, num_bpc;
> u8 dsc_bpc[3] = {};
> @@ -270,14 +334,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> return slots;
> }
>
> - intel_link_compute_m_n(crtc_state->dsc.compressed_bpp,
> - crtc_state->lane_count,
> - adjusted_mode->crtc_clock,
> - crtc_state->port_clock,
> - intel_dp_bw_fec_overhead(crtc_state->fec_enable),
> - &crtc_state->dp_m_n);
> - crtc_state->dp_m_n.tu = slots;
> -
> return 0;
> }
> static int intel_dp_mst_update_slots(struct intel_encoder *encoder,
> @@ -980,6 +1036,7 @@ intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
> if (ret)
> return ret;
>
> + /* TODO: also check if compression would allow for the mode */
> if (mode_rate > max_rate || mode->clock > max_dotclk ||
> drm_dp_calc_pbn_mode(mode->clock, min_bpp << 4) > port->full_pbn) {
> *status = MODE_CLOCK_HIGH;
> --
> 2.39.2
--
Ville Syrjälä
Intel
