drm/dp: device identification and quirks

Face the fact, there are Display Port sink and branch devices out there in the wild that don't follow the Display Port specifications, or they have bugs, or just otherwise require special treatment. Start a common quirk database the drivers can query based on the DP device identification. At least for now, we leave the workarounds for the drivers to implement as they see fit.

For starters, add a branch device that can't handle full 24-bit main link M and N attributes properly. Naturally, the workaround of reducing main link attributes for all devices ended up in regressions for other devices. So here we are.

v2: Rebase on DRM DP desc read helpers

Cc Ville Syrjälä <[email protected]>

Cc Dhinakaran Pandiyan <[email protected]>

Cc Clint Taylor <[email protected]>

Cc Adam Jackson <[email protected]>

Cc Harry Wentland <[email protected]>

Signed-off-by Jani Nikula <[email protected]>

---
  drivers/gpu/drm/drm_dp_helper.c | 52 +++++++++++++++++++++++++++++++++++++++--
  include/drm/drm_dp_helper.h     | 32 +++++++++++++++++++++++++
  2 files changed, 82 insertions(+), 2 deletions(-)

drivers/gpu/drm/drm_dp_helper.c +28 -0

index 52e0ca9a5bb1..8c3797283c3b 100644
@@ -1209,6 +1209,51 @@ int drm_dp_stop_crc(struct drm_dp_aux *aux)
  }
  EXPORT_SYMBOL(drm_dp_stop_crc);
 
+struct dpcd_quirk {
+	u8 oui[3];
+	bool is_branch;
+	u32 quirks;
+};
+
+#define OUI(first, second, third) { (first), (second), (third) }
+
+static const struct dpcd_quirk dpcd_quirk_list[] = {
+	/* Analogix 7737 needs reduced M and N at HBR2 link rates */
+	{ OUI(0x00, 0x22, 0xb9), true, BIT(DP_DPCD_QUIRK_LIMITED_M_N) },
+};
+
+#undef OUI
+
+/*
+ * Get a bit mask of DPCD quirks for the sink/branch device identified by
+ * ident. The quirk data is shared but it's up to the drivers to act on the
+ * data.
+ *
+ * For now, only the OUI (first three bytes) is used, but this may be extended
+ * to device identification string and hardware/firmware revisions later.
+ */
+static u32
+drm_dp_get_quirks(const struct drm_dp_dpcd_ident *ident, bool is_branch)
+{
+	const struct dpcd_quirk *quirk;
+	u32 quirks = 0;

drivers/gpu/drm/drm_dp_helper.c +12 -2

+
+		quirks |= quirk->quirks;
+	}
+
+	return quirks;
+}
+
  /**
   * drm_dp_read_desc - read sink/branch descriptor from DPCD
   * @aux: DisplayPort AUX channel

@@ -1231,14 +1276,17 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
  	if (ret < 0)
  		return ret;
 
+	desc->quirks = drm_dp_get_quirks(ident, is_branch);
+
  	dev_id_len = strnlen(ident->device_id, sizeof(ident->device_id));
 
-	DRM_DEBUG_KMS("DP %s: OUI %*phD dev-ID %*pE HW-rev %d.%d SW-rev %d.%d\n",
+	DRM_DEBUG_KMS("DP %s: OUI %*phD dev-ID %*pE HW-rev %d.%d SW-rev %d.%d quirks 0x%04x\n",
  		      is_branch ? "branch" : "sink",
  		      (int)sizeof(ident->oui), ident->oui,
  		      dev_id_len, ident->device_id,
  		      ident->hw_rev >> 4, ident->hw_rev & 0xf,
-		      ident->sw_major_rev, ident->sw_minor_rev);
+		      ident->sw_major_rev, ident->sw_minor_rev,
+		      desc->quirks);
 
  	return 0;
  }

include/drm/drm_dp_helper.h +23 -0

index aee5b96b51d7..717cb8496725 100644
@@ -1090,12 +1090,44 @@ struct drm_dp_dpcd_ident {
  /**
   * struct drm_dp_desc - DP branch/sink device descriptor
   * @ident: DP device identification from DPCD 0x400 (sink) or 0x500 (branch).
+ * @quirks: Quirks; use drm_dp_has_quirk() to query for the quirks.
   */
  struct drm_dp_desc {
  	struct drm_dp_dpcd_ident ident;
+	u32 quirks;
  };
 
  int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
  		     bool is_branch);
 
+/**
+ * enum drm_dp_quirk - Display Port sink/branch device specific quirks
+ *
+ * Display Port sink and branch devices in the wild have a variety of bugs, try
+ * to collect them here. The quirks are shared, but it's up to the drivers to
+ * implement workarounds for them.
+ */
+enum drm_dp_quirk {
+	/**
+	 * @DP_DPCD_QUIRK_LIMITED_M_N:
+	 *
+	 * The device requires main link attributes Mdiv and Ndiv to be limited
+	 * to 16 bits.
+	 */
+	DP_DPCD_QUIRK_LIMITED_M_N,
+};
+
+/**
+ * drm_dp_has_quirk() - does the DP device have a specific quirk
+ * @desc: Device decriptor filled by drm_dp_read_desc()
+ * @quirk: Quirk to query for

Switch to using the common DP helpers instead of using our own.

Signed-off-by Jani Nikula <[email protected]>

---
 drivers/gpu/drm/i915/intel_dp.c     | 37 ++++---------------------------------
 drivers/gpu/drm/i915/intel_drv.h    |  5 +----
 drivers/gpu/drm/i915/intel_lspcon.c |  2 +-
 3 files changed, 6 insertions(+), 38 deletions(-)

drivers/gpu/drm/i915/intel_dp.c +4 -33

index 4a6feb6a69bd..2a5f385e8f44 100644
@@ -1548,37 +1548,6 @@ static void intel_dp_print_rates(struct intel_dp *intel_dp)
 	DRM_DEBUG_KMS("common rates: %s\n", str);
 }
 
-bool
-__intel_dp_read_desc(struct intel_dp *intel_dp, struct intel_dp_desc *desc)
-{
-	u32 base = drm_dp_is_branch(intel_dp->dpcd) ? DP_BRANCH_OUI :
-						      DP_SINK_OUI;
-
-	return drm_dp_dpcd_read(&intel_dp->aux, base, desc, sizeof(*desc)) ==
-	       sizeof(*desc);
-}
-
-bool intel_dp_read_desc(struct intel_dp *intel_dp)
-{
-	struct intel_dp_desc *desc = &intel_dp->desc;
-	bool oui_sup = intel_dp->dpcd[DP_DOWN_STREAM_PORT_COUNT] &
-		       DP_OUI_SUPPORT;
-	int dev_id_len;
-
-	if (!__intel_dp_read_desc(intel_dp, desc))
-		return false;
-
-	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",
-		      (int)sizeof(desc->oui), desc->oui, oui_sup ? "" : "(NS)",
-		      dev_id_len, desc->device_id,
-		      desc->hw_rev >> 4, desc->hw_rev & 0xf,
-		      desc->sw_major_rev, desc->sw_minor_rev);
-
-	return true;
-}
-
 int
 intel_dp_max_link_rate(struct intel_dp *intel_dp)
 {

@@ -3662,7 +3631,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 	if (!intel_dp_read_dpcd(intel_dp))
 		return false;
 
-	intel_dp_read_desc(intel_dp);
+	drm_dp_read_desc(&intel_dp->aux, &intel_dp->desc,
+			 drm_dp_is_branch(intel_dp->dpcd));
 
 	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11)
 		dev_priv->no_aux_handshake = intel_dp->dpcd[DP_MAX_DOWNSPREAD] &

@@ -4677,7 +4647,8 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 
 	intel_dp_print_rates(intel_dp);
 
-	intel_dp_read_desc(intel_dp);
+	drm_dp_read_desc(&intel_dp->aux, &intel_dp->desc,
+			 drm_dp_is_branch(intel_dp->dpcd));
 
 	intel_dp_configure_mst(intel_dp);
 

drivers/gpu/drm/i915/intel_drv.h +1 -4

index bd500977b3fc..61a9981343d5 100644
@@ -996,7 +996,7 @@ struct intel_dp {
 	/* Max rate for the current link */
 	int max_link_rate;
 	/* sink or branch descriptor */
-	struct intel_dp_desc desc;
+	struct drm_dp_desc desc;
 	struct drm_dp_aux aux;
 	enum intel_display_power_domain aux_power_domain;
 	uint8_t train_set[4];

@@ -1571,9 +1571,6 @@ static inline unsigned int intel_dp_unused_lane_mask(int lane_count)
 }
 
 bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
-bool __intel_dp_read_desc(struct intel_dp *intel_dp,
-			  struct intel_dp_desc *desc);
-bool intel_dp_read_desc(struct intel_dp *intel_dp);
 int intel_dp_link_required(int pixel_clock, int bpp);
 int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
 bool intel_digital_port_connected(struct drm_i915_private *dev_priv,

drivers/gpu/drm/i915/intel_lspcon.c +1 -1

index 71cbe9c08932..5abef482eacf 100644
@@ -240,7 +240,7 @@ bool lspcon_init(struct intel_digital_port *intel_dig_port)
 		return false;
 	}
 
-	intel_dp_read_desc(dp);
+	drm_dp_read_desc(&dp->aux, &dp->desc, drm_dp_is_branch(dp->dpcd));
 
 	DRM_DEBUG_KMS("Success: LSPCON init\n");
 	return true;

Signature · 1 line

2.11.0

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

v2 by Jani: Rebased on the DP quirk database

v3 by Jani: Rebased on the reworked DP quirk database

Fixes 9a86cda07af2 ("drm/i915/dp: reduce link M/N parameters")

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93578
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100755

Cc Jani Nikula <[email protected]>

Cc Dhinakaran Pandiyan <[email protected]>

Cc Ville Syrjälä <[email protected]>

Signed-off-by Clint Taylor <[email protected]>

Signed-off-by Jani Nikula <[email protected]>

---
 drivers/gpu/drm/i915/i915_drv.h      |  3 ++-
 drivers/gpu/drm/i915/intel_display.c | 22 ++++++++++++++--------
 drivers/gpu/drm/i915/intel_dp.c      |  8 ++++++--
 drivers/gpu/drm/i915/intel_dp_mst.c  |  5 ++++-
 4 files changed, 26 insertions(+), 12 deletions(-)

drivers/gpu/drm/i915/i915_drv.h +2 -1

index a6f20471b4cd..699e07362044 100644
@@ -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:
  *

drivers/gpu/drm/i915/intel_display.c +14 -8

index 8217ed0e7132..ea4f116bd410 100644
@@ -6116,7 +6116,7 @@ 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) {

@@ -6292,7 +6292,8 @@ intel_reduce_m_n_ratio(uint32_t *num, uint32_t *den)
 }
 
 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

@@ -6300,9 +6301,11 @@ 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);

@@ -6313,16 +6316,19 @@ 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)

drivers/gpu/drm/i915/intel_dp.c +6 -2

index 2a5f385e8f44..1ae9de5cf39c 100644
@@ -1627,6 +1627,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 	int link_avail, link_clock;
 	int common_len;
 	uint8_t link_bw, rate_select;
+	bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
+					   DP_DPCD_QUIRK_LIMITED_M_N);
 
 	common_len = intel_dp_common_len_rate_limit(intel_dp,
 						    intel_dp->max_link_rate);

@@ -1759,7 +1761,8 @@ intel_dp_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,
+			       reduce_m_n);
 
 	if (intel_connector->panel.downclock_mode != NULL &&
 		dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) {

@@ -1767,7 +1770,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 			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,
+				reduce_m_n);
 	}
 
 	/*

drivers/gpu/drm/i915/intel_dp_mst.c +4 -1

index 68c788eb0b95..125917cebc60 100644
@@ -44,6 +44,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	int lane_count, slots;
 	const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
 	int mst_pbn;
+	bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
+					   DP_DPCD_QUIRK_LIMITED_M_N);
 
 	pipe_config->has_pch_encoder = false;
 	bpp = 24;

@@ -79,7 +81,8 @@ 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,
+			       reduce_m_n);
 
 	pipe_config->dp_m_n.tu = slots;
 

Signature · 1 line

2.11.0

Quoted 66 lines · Jani Nikula

Face the fact, there are Display Port sink and branch devices out there in the wild that don't follow the Display Port specifications, or they have bugs, or just otherwise require special treatment. Start a common quirk database the drivers can query based on the DP device identification. At least for now, we leave the workarounds for the drivers to implement as they see fit.

For starters, add a branch device that can't handle full 24-bit main link M and N attributes properly. Naturally, the workaround of reducing main link attributes for all devices ended up in regressions for other devices. So here we are.

v2: Rebase on DRM DP desc read helpers

Cc Ville Syrjälä <[email protected]>

Cc Dhinakaran Pandiyan <[email protected]>

Cc Clint Taylor <[email protected]>

Cc Adam Jackson <[email protected]>

Cc Harry Wentland <[email protected]>

Signed-off-by Jani Nikula <[email protected]>

---
  drivers/gpu/drm/drm_dp_helper.c | 52 +++++++++++++++++++++++++++++++++++++++--
  include/drm/drm_dp_helper.h     | 32 +++++++++++++++++++++++++
  2 files changed, 82 insertions(+), 2 deletions(-)

drivers/gpu/drm/drm_dp_helper.c +33 -0

index 52e0ca9a5bb1..8c3797283c3b 100644
@@ -1209,6 +1209,51 @@ int drm_dp_stop_crc(struct drm_dp_aux *aux)
  }
  EXPORT_SYMBOL(drm_dp_stop_crc);
 
+struct dpcd_quirk {
+	u8 oui[3];
+	bool is_branch;
+	u32 quirks;
+};
+
+#define OUI(first, second, third) { (first), (second), (third) }
+
+static const struct dpcd_quirk dpcd_quirk_list[] = {
+	/* Analogix 7737 needs reduced M and N at HBR2 link rates */
+	{ OUI(0x00, 0x22, 0xb9), true, BIT(DP_DPCD_QUIRK_LIMITED_M_N) },
+};
+
+#undef OUI
+
+/*
+ * Get a bit mask of DPCD quirks for the sink/branch device identified by
+ * ident. The quirk data is shared but it's up to the drivers to act on the
+ * data.
+ *
+ * For now, only the OUI (first three bytes) is used, but this may be extended
+ * to device identification string and hardware/firmware revisions later.
+ */
+static u32
+drm_dp_get_quirks(const struct drm_dp_dpcd_ident *ident, bool is_branch)
+{
+	const struct dpcd_quirk *quirk;
+	u32 quirks = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(dpcd_quirk_list); i++) {
+		quirk = &dpcd_quirk_list[i];
+

drivers/gpu/drm/drm_dp_helper.c int drm_dp_stop_crc(struct drm_dp_aux *aux) · line 1249

Quoted 5 lines

drivers/gpu/drm/drm_dp_helper.c +5 -0

+		if (quirk->is_branch != is_branch)
+			continue;
+
+		if (memcmp(quirk->oui, ident->oui, sizeof(ident->oui) != 0))
+			continue;

Oops, All branch devices appear to have the quirk applied. The memcmp should be closed before the !=0

if (memcmp(quirk->oui, ident->oui, sizeof(ident->oui)) != 0)

[  659.496861] [drm:drm_dp_read_desc] DP branch: OUI 00-1c-f8 dev-ID 
175IB0 HW-rev 1.0 SW-rev 7.32 quirks 0x0001
[  659.549017] [drm:drm_dp_read_desc] DP branch: OUI 00-22-b9 dev-ID 
7737 HW-rev 10.12 SW-rev 6.4 quirks 0x0001
[  659.630449] [drm:drm_dp_read_desc] DP sink: OUI ee-ff-c0 dev-ID \001 

HW-rev 0.0 SW-rev 0.0 quirks 0x0000

This was actually good to find out that LSPCON didn't like the reduced M and N from the quirk at HBR2.

-Clint

Quoted 79 lines

drivers/gpu/drm/drm_dp_helper.c +12 -2

+
+		quirks |= quirk->quirks;
+	}
+
+	return quirks;
+}
+
  /**
   * drm_dp_read_desc - read sink/branch descriptor from DPCD
   * @aux: DisplayPort AUX channel

@@ -1231,14 +1276,17 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
  	if (ret < 0)
  		return ret;
 
+	desc->quirks = drm_dp_get_quirks(ident, is_branch);
+
  	dev_id_len = strnlen(ident->device_id, sizeof(ident->device_id));
 
-	DRM_DEBUG_KMS("DP %s: OUI %*phD dev-ID %*pE HW-rev %d.%d SW-rev %d.%d\n",
+	DRM_DEBUG_KMS("DP %s: OUI %*phD dev-ID %*pE HW-rev %d.%d SW-rev %d.%d quirks 0x%04x\n",
  		      is_branch ? "branch" : "sink",
  		      (int)sizeof(ident->oui), ident->oui,
  		      dev_id_len, ident->device_id,
  		      ident->hw_rev >> 4, ident->hw_rev & 0xf,
-		      ident->sw_major_rev, ident->sw_minor_rev);
+		      ident->sw_major_rev, ident->sw_minor_rev,
+		      desc->quirks);
 
  	return 0;
  }

include/drm/drm_dp_helper.h +32 -0

index aee5b96b51d7..717cb8496725 100644
@@ -1090,12 +1090,44 @@ struct drm_dp_dpcd_ident {
  /**
   * struct drm_dp_desc - DP branch/sink device descriptor
   * @ident: DP device identification from DPCD 0x400 (sink) or 0x500 (branch).
+ * @quirks: Quirks; use drm_dp_has_quirk() to query for the quirks.
   */
  struct drm_dp_desc {
  	struct drm_dp_dpcd_ident ident;
+	u32 quirks;
  };
 
  int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
  		     bool is_branch);
 
+/**
+ * enum drm_dp_quirk - Display Port sink/branch device specific quirks
+ *
+ * Display Port sink and branch devices in the wild have a variety of bugs, try
+ * to collect them here. The quirks are shared, but it's up to the drivers to
+ * implement workarounds for them.
+ */
+enum drm_dp_quirk {
+	/**
+	 * @DP_DPCD_QUIRK_LIMITED_M_N:
+	 *
+	 * The device requires main link attributes Mdiv and Ndiv to be limited
+	 * to 16 bits.
+	 */
+	DP_DPCD_QUIRK_LIMITED_M_N,
+};
+
+/**
+ * drm_dp_has_quirk() - does the DP device have a specific quirk
+ * @desc: Device decriptor filled by drm_dp_read_desc()
+ * @quirk: Quirk to query for
+ *
+ * Return true if DP device identified by @desc has @quirk.
+ */
+static inline bool
+drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
+{
+	return desc->quirks & BIT(quirk);
+}
+
  #endif /* _DRM_DP_HELPER_H_ */