[Intel-gfx] [PATCH] drm/i915: Detect USB-C specific dongles before reducing M and N

[clinton.a.taylor at intel.com]

From: Clint Taylor <clinton.a.taylor at intel.com>

The Analogix 7737 DP to HDMI converter requires reduced N and M values when
to operate correctly at HBR2. Detect this IC by its OUI value of 0x0022B9.

Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>

Signed-off-by: Clint Taylor <clinton.a.taylor at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h      |  3 ++-
 drivers/gpu/drm/i915/intel_display.c | 22 ++++++++++++++--------
 drivers/gpu/drm/i915/intel_dp.c      | 22 ++++++++++++++++++++--
 drivers/gpu/drm/i915/intel_dp_mst.c  |  3 ++-
 drivers/gpu/drm/i915/intel_drv.h     |  1 +
 5 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 74dffbe..492e47e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -563,7 +563,8 @@ struct intel_link_m_n {
 
 void intel_link_compute_m_n(int bpp, int nlanes,
 			    int pixel_clock, int link_clock,
-			    struct intel_link_m_n *m_n);
+			    struct intel_link_m_n *m_n,
+				bool reduce_m_n);
 
 /* Interface history:
  *
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 7bcc604..8920a99 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6104,7 +6104,7 @@ 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);
+			       link_bw, &pipe_config->fdi_m_n, false);
 
 	ret = ironlake_check_fdi_lanes(dev, intel_crtc->pipe, pipe_config);
 	if (ret == -EINVAL && pipe_config->pipe_bpp > 6*3) {
@@ -6280,7 +6280,8 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
 }
 
 static void compute_m_n(unsigned int m, unsigned int n,
-			uint32_t *ret_m, uint32_t *ret_n)
+			uint32_t *ret_m, uint32_t *ret_n,
+			   bool reduce_m_n)
 {
 	/*
 	 * Reduce M/N as much as possible without loss in precision. Several DP
@@ -6288,9 +6289,11 @@ static void compute_m_n(unsigned int m, unsigned int n,
 	 * values. The passed in values are more likely to have the least
 	 * significant bits zero than M after rounding below, so do this first.
 	 */
-	while ((m & 1) == 0 && (n & 1) == 0) {
-		m >>= 1;
-		n >>= 1;
+	if (reduce_m_n) {
+		while ((m & 1) == 0 && (n & 1) == 0) {
+			m >>= 1;
+			n >>= 1;
+		}
 	}
 
 	*ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
@@ -6301,16 +6304,19 @@ static void compute_m_n(unsigned int m, unsigned int n,
 void
 intel_link_compute_m_n(int bits_per_pixel, int nlanes,
 		       int pixel_clock, int link_clock,
-		       struct intel_link_m_n *m_n)
+		       struct intel_link_m_n *m_n,
+			  bool reduce_m_n)
 {
 	m_n->tu = 64;
 
 	compute_m_n(bits_per_pixel * pixel_clock,
 		    link_clock * nlanes * 8,
-		    &m_n->gmch_m, &m_n->gmch_n);
+		    &m_n->gmch_m, &m_n->gmch_n,
+		    reduce_m_n);
 
 	compute_m_n(pixel_clock, link_clock,
-		    &m_n->link_m, &m_n->link_n);
+		    &m_n->link_m, &m_n->link_n,
+		    reduce_m_n);
 }
 
 static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 4a6feb6..f4c0582 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1548,6 +1548,20 @@ static void intel_dp_print_rates(struct intel_dp *intel_dp)
 	DRM_DEBUG_KMS("common rates: %s\n", str);
 }
 
+bool __intel_reduced_m_n(struct intel_dp *intel_dp)
+{
+	struct intel_dp_desc *desc = &intel_dp->desc;
+	bool ret = false;
+
+	/* Analogix 7737 needs reduced N and M at HBR2 link rates */
+	if (desc->oui[0] == 0x00 &&
+	    desc->oui[1] == 0x22 &&
+	    desc->oui[2] == 0xb9)
+		ret = true;
+
+	return ret;
+}
+
 bool
 __intel_dp_read_desc(struct intel_dp *intel_dp, struct intel_dp_desc *desc)
 {
@@ -1568,6 +1582,8 @@ bool intel_dp_read_desc(struct intel_dp *intel_dp)
 	if (!__intel_dp_read_desc(intel_dp, desc))
 		return false;
 
+	intel_dp->reduce_m_n = __intel_reduced_m_n(intel_dp);
+
 	dev_id_len = strnlen(desc->device_id, sizeof(desc->device_id));
 	DRM_DEBUG_KMS("DP %s: OUI %*phD%s dev-ID %*pE HW-rev %d.%d SW-rev %d.%d\n",
 		      drm_dp_is_branch(intel_dp->dpcd) ? "branch" : "sink",
@@ -1790,7 +1806,8 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
 	intel_link_compute_m_n(bpp, lane_count,
 			       adjusted_mode->crtc_clock,
 			       pipe_config->port_clock,
-			       &pipe_config->dp_m_n);
+			       &pipe_config->dp_m_n,
+				intel_dp->reduce_m_n);
 
 	if (intel_connector->panel.downclock_mode != NULL &&
 		dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) {
@@ -1798,7 +1815,8 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
 			intel_link_compute_m_n(bpp, lane_count,
 				intel_connector->panel.downclock_mode->clock,
 				pipe_config->port_clock,
-				&pipe_config->dp_m2_n2);
+				&pipe_config->dp_m2_n2,
+				intel_dp->reduce_m_n);
 	}
 
 	/*
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 68c788e..81fd8dc 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -79,7 +79,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	intel_link_compute_m_n(bpp, lane_count,
 			       adjusted_mode->crtc_clock,
 			       pipe_config->port_clock,
-			       &pipe_config->dp_m_n);
+			       &pipe_config->dp_m_n,
+				intel_dp->reduce_m_n);
 
 	pipe_config->dp_m_n.tu = slots;
 
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index e8de2f67..50e5077 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1057,6 +1057,7 @@ struct intel_dp {
 
 	/* Displayport compliance testing */
 	struct intel_dp_compliance compliance;
+	bool reduce_m_n;
 };
 
 struct intel_lspcon {
-- 
1.9.1