[PATCH 04/10] drm/i915/dp: Add M/N ratio check with warning for DP link config

[Suraj Kandpal <suraj.kandpal@intel.com>]

From: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

Introduce intel_dp_check_m_n_ratio() to validate the computed link
M/N ratio against the maximum allowed value. If the ratio exceeds the
limit, a warning is issued via drm_WARN().

The link config limits computed in the previous patches only restrict
the configurations that may be selected; this catches anything that
still slips through and turns a silently broken link into a loud
warning.

This check works off the M/N values as actually computed, which exposes
a mismatch with the prediction done while computing the limits: the
pixel clock there is the one before intel_dp_compute_config() divides
adjusted_mode->crtc_clock by the MSO link count. Divide in the
prediction too, so both agree. The joiner needs no such handling, as
intel_joiner_adjust_timings() only rewrites the pipe mode and leaves the
adjusted mode the link M/N is derived from untouched.

v2:
-Use the platform specific ratio limit. (Wa_14014191401)
-Use the MSO adjusted pixel clock when predicting the ratio, matching
what the link M/N is actually computed from. (Imre)
-Drop the check from ilk_fdi_compute_config(): it was passing dp_m_n
rather than the fdi_m_n it had just computed, and an FDI link cannot get
anywhere near the ratio limit anyway.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c     | 37 +++++++++++++++++++--
 drivers/gpu/drm/i915/display/intel_dp.h     |  3 ++
 drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 ++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 715314d3684e..585762be07bb 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1294,6 +1294,14 @@ intel_dp_can_support_m_n(struct intel_display *display,
 	return m_n_ratio <= max_m_n_ratio;
 }
 
+static int intel_dp_mso_pixel_clock(struct intel_dp *intel_dp, int pixel_clock)
+{
+	if (!intel_dp->mso_link_count)
+		return pixel_clock;
+
+	return pixel_clock / intel_dp->mso_link_count;
+}
+
 static
 bool intel_dp_can_join(struct intel_dp *intel_dp,
 		       int num_joined_pipes)
@@ -1488,7 +1496,9 @@ intel_dp_mode_valid(struct drm_connector *_connector,
 					      INTEL_DP_LINK_CAPS_ORDER_KEY_RATE_LANE,
 					      INTEL_DP_LINK_CAPS_FILTER_ALL,
 					      &max_rate_config) &&
-	    !intel_dp_can_support_m_n(display, target_clock, max_rate_config.rate))
+	    !intel_dp_can_support_m_n(display,
+				      intel_dp_mso_pixel_clock(intel_dp, target_clock),
+				      max_rate_config.rate))
 		return MODE_CLOCK_HIGH;
 
 	/*
@@ -2703,7 +2713,8 @@ intel_dp_compute_m_n_ratio_limits(struct intel_dp *intel_dp,
 	struct intel_dp_link_caps_order order =
 		intel_dp_link_caps_connector_compute_order(connector);
 	struct intel_dp_link_caps_filter new_filter = INTEL_DP_LINK_CAPS_FILTER_NONE;
-	int pixel_clock = intel_dp_mode_clock(crtc_state, conn_state);
+	int pixel_clock = intel_dp_mso_pixel_clock(intel_dp,
+						  intel_dp_mode_clock(crtc_state, conn_state));
 	struct intel_dp_link_config link_config;
 	struct intel_dp_link_caps_iter iter;
 	bool found = false;
@@ -3362,6 +3373,24 @@ static bool can_enable_drrs(struct intel_connector *connector,
 		intel_panel_drrs_type(connector) == DRRS_TYPE_SEAMLESS;
 }
 
+void intel_dp_check_m_n_ratio(struct intel_crtc_state *crtc_state,
+			      struct intel_link_m_n *m_n)
+{
+	struct intel_display *display = to_intel_display(crtc_state);
+	int max_m_n_ratio = intel_dp_get_max_m_n_ratio(display);
+	int m_n_ratio;
+
+	if (!m_n || !m_n->link_n)
+		return;
+
+	m_n_ratio = DIV_ROUND_UP(m_n->link_m, m_n->link_n);
+
+	if (m_n_ratio > max_m_n_ratio)
+		drm_WARN(display->drm, 1,
+			 "Link M/N ratio (%d) exceeds max allowed (%d)\n",
+			 m_n_ratio, max_m_n_ratio);
+}
+
 static void
 intel_dp_drrs_compute_config(struct intel_connector *connector,
 			     struct intel_crtc_state *pipe_config,
@@ -3400,6 +3429,8 @@ intel_dp_drrs_compute_config(struct intel_connector *connector,
 			       intel_dp_bw_fec_overhead(pipe_config->fec_enable),
 			       &pipe_config->dp_m2_n2);
 
+	intel_dp_check_m_n_ratio(pipe_config, &pipe_config->dp_m2_n2);
+
 	/* FIXME: abstract this better */
 	if (pipe_config->splitter.enable)
 		pipe_config->dp_m2_n2.data_m *= pipe_config->splitter.link_count;
@@ -3719,6 +3750,8 @@ intel_dp_compute_config(struct intel_atomic_state *state,
 				       pipe_config->port_clock,
 				       intel_dp_bw_fec_overhead(pipe_config->fec_enable),
 				       &pipe_config->dp_m_n);
+
+		intel_dp_check_m_n_ratio(pipe_config, &pipe_config->dp_m_n);
 	}
 
 	ret = intel_dp_compute_min_hblank(pipe_config, conn_state);
diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
index 757e74ca8696..13e9432f98c6 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.h
+++ b/drivers/gpu/drm/i915/display/intel_dp.h
@@ -26,6 +26,7 @@ struct intel_display;
 struct intel_dp;
 struct intel_dp_link_config;
 struct intel_encoder;
+struct intel_link_m_n;
 
 struct link_config_limits {
 	struct intel_dp_link_caps_filter link_config_filter;
@@ -244,5 +245,7 @@ void intel_dp_link_cleanup(struct intel_dp *intel_dp);
 
 bool intel_dp_can_support_m_n(struct intel_display *display,
 			      int pixel_clock, int link_rate);
+void intel_dp_check_m_n_ratio(struct intel_crtc_state *crtc_state,
+			      struct intel_link_m_n *m_n);
 
 #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 796374cebf05..4faa0a86dda3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -347,6 +347,8 @@ int intel_dp_mtp_tu_compute_config(struct intel_dp *intel_dp,
 					 link_bpp_x16,
 					 &crtc_state->dp_m_n);
 
+		intel_dp_check_m_n_ratio(crtc_state, &crtc_state->dp_m_n);
+
 		if (is_mst) {
 			int remote_bw_overhead;
 			int remote_tu;
-- 
2.34.1