[PATCHv3] drm/i915/dp: Guarantee a minimum HBlank time

[Arun R Murthy]

Mandate a minimum Hblank symbol cycle count between BS and BE in 8b/10b
MST and 12b/132b mode.
Spec: DP2.1a

v2: Affine calculation/updation of min HBlank to dp_mst (Jani)
v3: moved min_hblank from struct intel_dp to intel_crtc_state (Jani)

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_atomic.c   |  1 +
 drivers/gpu/drm/i915/display/intel_crtc.c     |  1 +
 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_dp_mst.c   | 28 +++++++++++++++++++
 drivers/gpu/drm/i915/i915_reg.h               |  4 +++
 5 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_atomic.c b/drivers/gpu/drm/i915/display/intel_atomic.c
index 03dc54c802d3..24aa079efcad 100644
--- a/drivers/gpu/drm/i915/display/intel_atomic.c
+++ b/drivers/gpu/drm/i915/display/intel_atomic.c
@@ -278,6 +278,7 @@ intel_crtc_duplicate_state(struct drm_crtc *crtc)
 	crtc_state->dsb_color_vblank = NULL;
 	crtc_state->dsb_commit = NULL;
 	crtc_state->use_dsb = false;
+	crtc_state->min_hblank = 0;
 
 	return &crtc_state->uapi;
 }
diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
index 3c9168a57f38..472f3010bce4 100644
--- a/drivers/gpu/drm/i915/display/intel_crtc.c
+++ b/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -184,6 +184,7 @@ void intel_crtc_state_reset(struct intel_crtc_state *crtc_state,
 	crtc_state->scaler_state.scaler_id = -1;
 	crtc_state->mst_master_transcoder = INVALID_TRANSCODER;
 	crtc_state->max_link_bpp_x16 = INT_MAX;
+	crtc_state->min_hblank = 0;
 }
 
 static struct intel_crtc *intel_crtc_alloc(void)
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 2bb1fa64da2f..7f631fef128e 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -1075,6 +1075,7 @@ struct intel_crtc_state {
 
 	int max_link_bpp_x16;	/* in 1/16 bpp units */
 	int pipe_bpp;		/* in 1 bpp units */
+	int min_hblank;		/* min HBlank for DP2.1 */
 	struct intel_link_m_n dp_m_n;
 
 	/* m2_n2 for eDP downclock */
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 1a2ff3e1cb68..2e088760a23a 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -161,6 +161,28 @@ static int intel_dp_mst_dsc_get_slice_count(const struct intel_connector *connec
 					    num_joined_pipes);
 }
 
+static void intel_dp_mst_compute_min_hblank(struct intel_crtc_state *crtc_state,
+					    struct intel_connector *intel_connector,
+					    int bpp_x16)
+{
+	struct intel_encoder *intel_encoder = intel_connector->encoder;
+	struct intel_display *intel_display = to_intel_display(intel_encoder);
+	const struct drm_display_mode *adjusted_mode =
+					&crtc_state->hw.adjusted_mode;
+	u32 symbol_size = intel_dp_is_uhbr(crtc_state) ? 32 : 8;
+	u32 hblank;
+
+	if (DISPLAY_VER(intel_display) < 20)
+		return;
+
+	/* Calculate min Hblank Link Layer Symbol Cycle Count for 8b/10b MST & 128b/132b */
+	hblank = DIV_ROUND_UP((DIV_ROUND_UP(adjusted_mode->htotal - adjusted_mode->hdisplay, 4) * bpp_x16), symbol_size);
+	if (intel_dp_is_uhbr(crtc_state))
+		crtc_state->min_hblank = (hblank > 5) ? hblank : 5;
+	else
+		crtc_state->min_hblank = (hblank > 3) ? hblank : 3;
+}
+
 static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 						struct intel_crtc_state *crtc_state,
 						int max_bpp,
@@ -238,6 +260,8 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 		remote_bw_overhead = intel_dp_mst_bw_overhead(crtc_state, connector,
 							      true, dsc_slice_count, link_bpp_x16);
 
+		intel_dp_mst_compute_min_hblank(crtc_state, connector, link_bpp_x16);
+
 		intel_dp_mst_compute_m_n(crtc_state, connector,
 					 local_bw_overhead,
 					 link_bpp_x16,
@@ -1292,6 +1316,10 @@ static void intel_mst_enable_dp(struct intel_atomic_state *state,
 			       TRANS_DP2_VFREQ_PIXEL_CLOCK(crtc_clock_hz & 0xffffff));
 	}
 
+	if (DISPLAY_VER(dev_priv) >= 20)
+		intel_de_write(dev_priv, DP_MIN_HBLANK_CTL(dev_priv, trans),
+			       pipe_config->min_hblank);
+
 	enable_bs_jitter_was(pipe_config);
 
 	intel_ddi_enable_transcoder_func(encoder, pipe_config);
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 405f409e9761..8aeed48f9170 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1147,6 +1147,10 @@
 #define _TRANS_MULT_B		0x6102c
 #define TRANS_MULT(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _TRANS_MULT_A)
 
+#define _DP_MIN_HBLANK_CTL_A	0x600ac
+#define _DP_MIN_HBLANK_CTL_B	0x610ac
+#define DP_MIN_HBLANK_CTL(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _DP_MIN_HBLANK_CTL_A)
+
 /* VGA port control */
 #define ADPA			_MMIO(0x61100)
 #define PCH_ADPA                _MMIO(0xe1100)
-- 
2.25.1