[Intel-gfx] [PATCH v2 10/22] drm/dp_mst: Add a way to calculate PBN values with FEC overhead

[Imre Deak <imre.deak@intel.com>]

Add a way for drivers to calculate the MST PBN values with FEC overhead.
This is required by 8b/10b links both for DSC and non-DSC (the latter
needed if there are both DSC and non-DSC streams on the same MST link).

Also add kunit test cases for PBN values calculated with FEC overhead.

Cc: Lyude Paul <lyude@redhat.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Wayne Lin <wayne.lin@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  2 +-
 .../display/amdgpu_dm/amdgpu_dm_mst_types.c   |  2 +-
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 18 +++++++++++----
 drivers/gpu/drm/i915/display/intel_dp_mst.c   |  5 ++--
 drivers/gpu/drm/nouveau/dispnv50/disp.c       |  2 +-
 .../gpu/drm/tests/drm_dp_mst_helper_test.c    | 23 ++++++++++++++++++-
 include/drm/display/drm_dp_mst_helper.h       |  2 +-
 7 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 268cb99a4c4bc..22868d6eb8977 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -6782,7 +6782,7 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder,
 								    max_bpc);
 		bpp = convert_dc_color_depth_into_bpc(color_depth) * 3;
 		clock = adjusted_mode->clock;
-		dm_new_connector_state->pbn = drm_dp_calc_pbn_mode(clock, bpp, false);
+		dm_new_connector_state->pbn = drm_dp_calc_pbn_mode(clock, bpp, false, false);
 	}
 
 	dm_new_connector_state->vcpi_slots =
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 57230661132bd..9acfdefc792d6 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -1636,7 +1636,7 @@ enum dc_status dm_dp_mst_is_port_support_mode(
 	} else {
 		/* check if mode could be supported within full_pbn */
 		bpp = convert_dc_color_depth_into_bpc(stream->timing.display_color_depth) * 3;
-		pbn = drm_dp_calc_pbn_mode(stream->timing.pix_clk_100hz / 10, bpp, false);
+		pbn = drm_dp_calc_pbn_mode(stream->timing.pix_clk_100hz / 10, bpp, false, false);
 
 		if (pbn > aconnector->mst_output_port->full_pbn)
 			return DC_FAIL_BANDWIDTH_VALIDATE;
diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index bd0f35a0ea5fb..e26f1b7f5a701 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -4693,26 +4693,34 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
  * @clock: dot clock for the mode
  * @bpp: bpp for the mode.
  * @dsc: DSC mode. If true, bpp has units of 1/16 of a bit per pixel
+ * @fec: FEC overhead.
  *
  * This uses the formula in the spec to calculate the PBN value for a mode.
  */
-int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
+int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc, bool fec)
 {
 	/*
-	 * margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
+	 * Overheads:
+	 * - SSC downspread and ref clock variation margin:
+	 *     5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
+	 * - FEC symbol insertions:
+	 *     2.4% as per spec, factor is 1.024
+	 *
 	 * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
 	 * common multiplier to render an integer PBN for all link rate/lane
 	 * counts combinations
 	 * calculate
-	 * peak_kbps *= (1006/1000)
+	 * peak_kbps *= (1006/1000) without FEC, or
+	 * peak_kbps *= (1030/1000) with FEC
 	 * peak_kbps *= (64/54)
-	 * peak_kbps *= 8    convert to bytes
+	 * peak_kbps /= 8    convert to bytes
 	 *
 	 * If the bpp is in units of 1/16, further divide by 16. Put this
 	 * factor in the numerator rather than the denominator to avoid
 	 * integer overflow
 	 */
-	u32 bpp_m = (dsc ? 64 / 16 : 64) * 1006 * bpp;
+	u32 overhead = fec ? 1030 : 1006;
+	u32 bpp_m = (dsc ? 64 / 16 : 64) * overhead * bpp;
 
 	return DIV_ROUND_UP_ULL(mul_u32_u32(clock, bpp_m),
 				8 * 54 * 1000 * 1000);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 525766206fce5..6eeb7dbf5ba67 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -110,7 +110,8 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 
 		crtc_state->pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock,
 						       dsc ? bpp << 4 : bpp,
-						       dsc);
+						       dsc,
+						       false);
 
 		slots = drm_dp_atomic_find_time_slots(state, &intel_dp->mst_mgr,
 						      connector->port,
@@ -983,7 +984,7 @@ intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
 		return ret;
 
 	if (mode_rate > max_rate || mode->clock > max_dotclk ||
-	    drm_dp_calc_pbn_mode(mode->clock, min_bpp, false) > port->full_pbn) {
+	    drm_dp_calc_pbn_mode(mode->clock, min_bpp, false, false) > port->full_pbn) {
 		*status = MODE_CLOCK_HIGH;
 		return 0;
 	}
diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 4e7c9c353c511..d71c28e458107 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -967,7 +967,7 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
 
 		asyh->or.bpc = connector->display_info.bpc;
 		asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, asyh->or.bpc * 3,
-						    false);
+						    false, false);
 	}
 
 	mst_state = drm_atomic_get_mst_topology_state(state, &mstm->mgr);
diff --git a/drivers/gpu/drm/tests/drm_dp_mst_helper_test.c b/drivers/gpu/drm/tests/drm_dp_mst_helper_test.c
index ea2182815ebe8..3c0c0ffd5f9f5 100644
--- a/drivers/gpu/drm/tests/drm_dp_mst_helper_test.c
+++ b/drivers/gpu/drm/tests/drm_dp_mst_helper_test.c
@@ -16,6 +16,7 @@ struct drm_dp_mst_calc_pbn_mode_test {
 	const int clock;
 	const int bpp;
 	const bool dsc;
+	const bool fec;
 	const int expected;
 };
 
@@ -24,39 +25,59 @@ static const struct drm_dp_mst_calc_pbn_mode_test drm_dp_mst_calc_pbn_mode_cases
 		.clock = 154000,
 		.bpp = 30,
 		.dsc = false,
+		.fec = false,
 		.expected = 689
 	},
 	{
 		.clock = 234000,
 		.bpp = 30,
 		.dsc = false,
+		.fec = false,
 		.expected = 1047
 	},
 	{
 		.clock = 297000,
 		.bpp = 24,
 		.dsc = false,
+		.fec = false,
 		.expected = 1063
 	},
 	{
 		.clock = 332880,
 		.bpp = 24 << 4,
 		.dsc = true,
+		.fec = false,
 		.expected = 1191
 	},
 	{
 		.clock = 324540,
 		.bpp = 24 << 4,
 		.dsc = true,
+		.fec = false,
 		.expected = 1161
 	},
+	{
+		.clock = 324540,
+		.bpp = 24 << 4,
+		.dsc = true,
+		.fec = true,
+		.expected = 1189
+	},
+	{
+		.clock = 324540,
+		.bpp = 24,
+		.dsc = false,
+		.fec = true,
+		.expected = 1189
+	},
 };
 
 static void drm_test_dp_mst_calc_pbn_mode(struct kunit *test)
 {
 	const struct drm_dp_mst_calc_pbn_mode_test *params = test->param_value;
 
-	KUNIT_EXPECT_EQ(test, drm_dp_calc_pbn_mode(params->clock, params->bpp, params->dsc),
+	KUNIT_EXPECT_EQ(test, drm_dp_calc_pbn_mode(params->clock, params->bpp,
+						   params->dsc, params->fec),
 			params->expected);
 }
 
diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
index ed5c9660563c4..0953b7b16a51b 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -832,7 +832,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector,
 int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
 			     int link_rate, int link_lane_count);
 
-int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc);
+int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc, bool fec);
 
 void drm_dp_mst_update_slots(struct drm_dp_mst_topology_state *mst_state, uint8_t link_encoding_cap);
 
-- 
2.37.2