[PATCH v9 0/5] Add SCDC information to connector debugfs

[PATCH v9 0/5] Add SCDC information to connector debugfs

[Nicolas Frattaroli]

HDMI uses the DDC I2C bus for communicating various bits of link status
out of band with the actual HDMI video signal. This information can be
useful for debugging issues like questionable cables sabotaged by feline
teeth, Enthusiast Grade cables made of cow fencing wire, and other such
problems that ruin one's media viewing plans.

Consequently, this series exposes various bits of pertinent information
from the SCDC protocol in an HDMI connector's debugfs. To continually
poll the link status, userspace can poll the debugfs file.

---
Changes in v9:
- Unlock mode_config.mutex on disconnected connector early exit
- Calculate and print Reed-Solomon error corrections counter on != 4
  lane FRL as well. Technically a functional change to an already
  reviewed patch, but I kept the R-b because it's so minor.
- Link to v8: https://patch.msgid.link/20260722-scdc-link-health-v8-0-cd1dacbb85d9@collabora.com

Changes in v8:
- Acquire mode_config mutex in an interruptible way during
  scdc_status_show to avoid racing connector state
- Remove scdc_debugfs_priv, use connector as debugfs entry priv instead
- Allocate and free state in scdc_status_show, since it doesn't need to
  persist across debugfs reads
- Check for NULL ddc in drm_scdc_read_state in the unlikely event an
  EDID with the SCDC flag was forced on a connector with no DDC
- Note: drm_connector_get() is omitted from drm_scdc_debugfs_init
  because drm_scdc_debugfs_init is called on connector construction and
  the debugfs is removed on connector destruction. Adding a redundant
  reference increase here would necessitate introducing a destruction
  callback to mirror the debugfs_init connector op for the sole purpose
  of decreasing the counter again.
- Link to v7: https://patch.msgid.link/20260721-scdc-link-health-v7-0-92df1b6ad5fc@collabora.com

Changes in v7:
- Move HDMI debugfs registration to new state helper, fix up all users
  (sun4i, vc4, bridge)
- Register scdc debugfs in new hdmi debugfs helper
- Link to v6: https://patch.msgid.link/20260611-scdc-link-health-v6-0-6307875a6b5e@collabora.com

Changes in v6:
- Fix off-by-one error in drm_scdc_read_state
- Link to v5: https://patch.msgid.link/20260604-scdc-link-health-v5-0-11173b0ac3de@collabora.com

Changes in v5:
- Read all SCDC data regardless of update flags
- Dump SCDC data as hex before the human-readable output. It's separated
  with "\n----------------\n\n".
- No longer write 0 to read-only registers
- Add Reed-Solomon Corrections counter parsing
- Parsing has been kept. A desire was expressed to get this data without
  any external userspace tooling, and the kernel will need to parse it
  eventually anyway to set the link status.
- Functions have been made static as of right now, since external users
  may do another pass over the function signatures anyway.
- Link to v4: https://patch.msgid.link/20260527-scdc-link-health-v4-0-622ea40a1f59@collabora.com

Changes in v4:
- Don't use C struct bitfields for parsing status flags. Switch to
  bitwise AND for boolean flags, and FIELD_GET for multi-bit values.
- Drop the superfluous !! and parens
- Drop the __pure attributes on static functions
- Initialise stack local arrays with {}, not { 0 }.
- I've kept the print macros and %-30s format. Reason being that I don't
  want to repeat the format specifier and str_yes_no(foo) a bunch, and I
  like the %-30s format because it means all values are aligned with the
  value of the longest field, which is 30 chars long.
- Link to v3: https://patch.msgid.link/20260526-scdc-link-health-v3-0-59e4a4aaead1@collabora.com

Changes in v3:
- Add patch to change return type of drm_scdc_read/write.
- Rework error counter reading to duplicate less code.
- Also check lane 3 counter valid flag when reading its error counter.
- Use memset to clear buf for error counters, rather than doing it in
  the loop.
- Make read_error_counters not accept 0 as num_lanes; fix it up in the
  caller instead.
- Link to v2: https://patch.msgid.link/20260520-scdc-link-health-v2-0-511af18cd64b@collabora.com

Changes in v2:
- Add HDMI 2.1 SCDC status reporting
- Link to v1: https://patch.msgid.link/20260415-scdc-link-health-v1-0-8e731e88eaf0@collabora.com

To: Jani Nikula <jani.nikula@linux.intel.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
To: Andrzej Hajda <andrzej.hajda@intel.com>
To: Neil Armstrong <neil.armstrong@linaro.org>
To: Robert Foss <rfoss@kernel.org>
To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
To: Jonas Karlman <jonas@kwiboo.se>
To: Jernej Skrabec <jernej.skrabec@gmail.com>
To: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Daniel Stone <daniel@fooishbar.org>
To: Hans Verkuil <hverkuil+cisco@kernel.org>
To: Chen-Yu Tsai <wens@kernel.org>
To: Samuel Holland <samuel@sholland.org>
To: Dave Stevenson <dave.stevenson@raspberrypi.com>
To: Maíra Canal <mcanal@igalia.com>
To: Raspberry Pi Kernel Maintenance <kernel-list@raspberrypi.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel@collabora.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-sunxi@lists.linux.dev
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

---
Nicolas Frattaroli (5):
      drm/scdc-helper: Don't use ssize_t return type for scdc_read/write
      drm/scdc-helper: Add scdc_status debugfs entry
      drm/scdc-helper: Implement parsing and printing HDMI 2.1 fields
      drm/debugfs: Move HDMI debugfs registration to state helper
      drm/display: hdmi-state-helper: Init SCDC debugfs for HDMI

 drivers/gpu/drm/display/drm_bridge_connector.c  |   3 +
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 156 +++++++++++++
 drivers/gpu/drm/display/drm_scdc_helper.c       | 289 +++++++++++++++++++++++-
 drivers/gpu/drm/drm_debugfs.c                   | 157 -------------
 drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c          |   1 +
 drivers/gpu/drm/vc4/vc4_hdmi.c                  |   1 +
 include/drm/display/drm_hdmi_state_helper.h     |   3 +
 include/drm/display/drm_scdc.h                  |  21 +-
 include/drm/display/drm_scdc_helper.h           | 103 ++++++++-
 9 files changed, 568 insertions(+), 166 deletions(-)
---
base-commit: b747a63003130bef1a3d5d6ba97c94d0cee36f55
change-id: 20260413-scdc-link-health-89326013d96c

Best regards,
--  
Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

[PATCH v9 1/5] drm/scdc-helper: Don't use ssize_t return type for scdc_read/write

[Nicolas Frattaroli]

drm_scdc_read and drm_scdc_write, both of which are only used within
drm_scdc_helper (although exported), use a ssize_t as their return type.

This would make sense if they returned the number of bytes read/written
on success, and negative errno otherwise. However, they return 0 on
success.

Demote them to "int" as their return type, in order to avoid needlessly
using 64 bits when less suffices.

No functional change.

Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/display/drm_scdc_helper.c | 8 ++++----
 include/drm/display/drm_scdc_helper.h     | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c b/drivers/gpu/drm/display/drm_scdc_helper.c
index df878aad4a36..8403f2390ab6 100644
--- a/drivers/gpu/drm/display/drm_scdc_helper.c
+++ b/drivers/gpu/drm/display/drm_scdc_helper.c
@@ -67,8 +67,8 @@
  * Returns:
  * 0 on success, negative error code on failure.
  */
-ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
-		      size_t size)
+int drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
+		  size_t size)
 {
 	int ret;
 	struct i2c_msg msgs[2] = {
@@ -107,8 +107,8 @@ EXPORT_SYMBOL(drm_scdc_read);
  * Returns:
  * 0 on success, negative error code on failure.
  */
-ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
-		       const void *buffer, size_t size)
+int drm_scdc_write(struct i2c_adapter *adapter, u8 offset, const void *buffer,
+		   size_t size)
 {
 	struct i2c_msg msg = {
 		.addr = SCDC_I2C_SLAVE_ADDRESS,
diff --git a/include/drm/display/drm_scdc_helper.h b/include/drm/display/drm_scdc_helper.h
index 34600476a1b9..e9ccaeba56dd 100644
--- a/include/drm/display/drm_scdc_helper.h
+++ b/include/drm/display/drm_scdc_helper.h
@@ -31,10 +31,10 @@
 struct drm_connector;
 struct i2c_adapter;
 
-ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
-		      size_t size);
-ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
-		       const void *buffer, size_t size);
+int drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
+		  size_t size);
+int drm_scdc_write(struct i2c_adapter *adapter, u8 offset, const void *buffer,
+		   size_t size);
 
 /**
  * drm_scdc_readb - read a single byte from SCDC

-- 
2.55.0

[PATCH v9 2/5] drm/scdc-helper: Add scdc_status debugfs entry

[Nicolas Frattaroli]

SCDC provides status information on the current display link. At the
very least, it may be useful to expose this info through debugfs.

Add a debugfs entry for it under the connector, which displays a few
more details parsed out of the SCDC registers. A new
drm_scdc_debugfs_init function can be called by the connector
implementation to initialise the debugfs file.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/display/drm_scdc_helper.c | 186 ++++++++++++++++++++++++++++++
 include/drm/display/drm_scdc_helper.h     |  32 +++++
 2 files changed, 218 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c b/drivers/gpu/drm/display/drm_scdc_helper.c
index 8403f2390ab6..129a2b85527b 100644
--- a/drivers/gpu/drm/display/drm_scdc_helper.c
+++ b/drivers/gpu/drm/display/drm_scdc_helper.c
@@ -24,7 +24,9 @@
 #include <linux/export.h>
 #include <linux/i2c.h>
 #include <linux/slab.h>
+#include <linux/debugfs.h>
 #include <linux/delay.h>
+#include <linux/overflow.h>
 
 #include <drm/display/drm_scdc_helper.h>
 #include <drm/drm_connector.h>
@@ -276,3 +278,187 @@ bool drm_scdc_set_high_tmds_clock_ratio(struct drm_connector *connector,
 	return true;
 }
 EXPORT_SYMBOL(drm_scdc_set_high_tmds_clock_ratio);
+
+static void
+drm_scdc_parse_status0_flags(u8 val, struct drm_scdc_status_flags *flags)
+{
+	flags->clock_detected = val & SCDC_CLOCK_DETECT;
+	flags->ch0_locked = val & SCDC_CH0_LOCK;
+	flags->ch1_locked = val & SCDC_CH1_LOCK;
+	flags->ch2_locked = val & SCDC_CH2_LOCK;
+}
+
+static int drm_scdc_parse_error_counters(const u8 scdc[256], u16 counter[3])
+{
+	u8 sum = 0;
+	int i;
+
+	for (i = SCDC_ERR_DET_0_L; i <= SCDC_ERR_DET_CHECKSUM ; i++)
+		sum = wrapping_add(u8, sum, scdc[i]);
+
+	if (sum)
+		return -EPROTO;
+
+	for (i = 0; i < 3; i++) {
+		if (scdc[SCDC_ERR_DET_0_H + i * 2] & SCDC_CHANNEL_VALID)
+			counter[i] =  (scdc[SCDC_ERR_DET_0_H + i * 2] &
+				       ~SCDC_CHANNEL_VALID) << 8 |
+				       scdc[SCDC_ERR_DET_0_L + i * 2];
+		else
+			counter[i] = 0;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_scdc_read_state - Update state from SCDC
+ * @connector: pointer to a &struct drm_connector on which to operate on
+ * @state: pointer to a &struct drm_scdc_state to fill
+ *
+ * Reads the entire 256 byte SCDC state and parses it.
+ *
+ * Returns: %0 on success, negative errno on failure.
+ */
+int drm_scdc_read_state(struct drm_connector *connector, struct drm_scdc_state *state)
+{
+	struct i2c_adapter *ddc;
+	struct drm_scdc *scdc;
+	u8 *buf = state->scdc;
+	int ret;
+
+	if (!state || !connector)
+		return -ENODEV;
+
+	scdc = &connector->display_info.hdmi.scdc;
+	ddc = connector->ddc;
+
+	if (!scdc->supported || !ddc)
+		return -EOPNOTSUPP;
+
+	/* Read in 128-byte chunks, to work around DP<->HDMI converters with issues. */
+	ret = drm_scdc_read(ddc, 0, buf, 128);
+	if (ret)
+		return ret;
+
+	ret = drm_scdc_read(ddc, 128, &buf[128], 128);
+	if (ret)
+		return ret;
+
+	state->scrambling_enabled = buf[SCDC_TMDS_CONFIG] & SCDC_SCRAMBLING_ENABLE;
+	state->tmds_bclk_x40 = buf[SCDC_TMDS_CONFIG] & SCDC_TMDS_BIT_CLOCK_RATIO_BY_40;
+
+	state->scrambling_detected = buf[SCDC_SCRAMBLER_STATUS] & SCDC_SCRAMBLING_STATUS;
+
+	drm_scdc_parse_status0_flags(buf[SCDC_STATUS_FLAGS_0], &state->stf);
+	ret = drm_scdc_parse_error_counters(buf, state->error_count);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_scdc_read_state);
+
+#define scdc_print_str(_f, key, s) \
+	(seq_printf((_f), "%-30s: %s\n", (key), (s)))
+#define scdc_print_flag(_f, key, val) \
+	(scdc_print_str((_f), (key), str_yes_no((val))))
+#define scdc_print_dec(_f, key, val) \
+	(seq_printf((_f), "%-30s: %d\n", (key), (val)))
+
+static int scdc_status_show(struct seq_file *m, void *data)
+{
+	struct drm_connector *connector = m->private;
+	struct drm_scdc *scdc = &connector->display_info.hdmi.scdc;
+	struct drm_scdc_state *st;
+	int i, ret;
+
+	drm_connector_get(connector);
+
+	ret = mutex_lock_interruptible(&connector->dev->mode_config.mutex);
+	if (ret)
+		goto err_conn_put;
+
+	if (connector->status != connector_status_connected) {
+		ret = -ENODEV;
+		goto err_unlock;
+	}
+
+	if (scdc->supported) {
+		st = kzalloc_obj(*st);
+		if (!st) {
+			ret = -ENOMEM;
+			goto err_unlock;
+		}
+		ret = drm_scdc_read_state(connector, st);
+		if (ret)
+			goto err_free_state;
+
+		for (i = 0; i < ARRAY_SIZE(st->scdc); i += 16)
+			seq_printf(m, "%*ph\n", 16, &st->scdc[i]);
+
+		seq_puts(m, "\n----------------\n\n");
+	}
+
+	scdc_print_flag(m, "SCDC Supported", scdc->supported);
+	if (!scdc->supported) {
+		ret = 0;
+		goto err_unlock;
+	}
+
+	scdc_print_flag(m, "Sink Read Request Capable", scdc->read_request);
+	scdc_print_flag(m, "Scrambling Supported", scdc->scrambling.supported);
+	scdc_print_flag(m, "Low Rate Scrambling Supported", scdc->scrambling.low_rates);
+
+	mutex_unlock(&connector->dev->mode_config.mutex);
+
+	drm_connector_put(connector);
+
+	scdc_print_flag(m, "Scrambling Enabled", st->scrambling_enabled);
+	scdc_print_flag(m, "Scrambling Detected", st->scrambling_detected);
+
+	if (st->tmds_bclk_x40)
+		scdc_print_str(m, "TMDS Bit Clock Ratio", "1/40");
+	else
+		scdc_print_str(m, "TMDS Bit Clock Ratio", "1/10");
+
+	scdc_print_flag(m, "Clock Detected", st->stf.clock_detected);
+	scdc_print_flag(m, "Channel 0 Locked", st->stf.ch0_locked);
+	scdc_print_flag(m, "Channel 1 Locked", st->stf.ch1_locked);
+	scdc_print_flag(m, "Channel 2 Locked", st->stf.ch2_locked);
+
+	scdc_print_dec(m, "Channel 0 Errors", st->error_count[0]);
+	scdc_print_dec(m, "Channel 1 Errors", st->error_count[1]);
+	scdc_print_dec(m, "Channel 2 Errors", st->error_count[2]);
+
+	kfree(st);
+
+	return 0;
+
+err_free_state:
+	kfree(st);
+err_unlock:
+	mutex_unlock(&connector->dev->mode_config.mutex);
+err_conn_put:
+	drm_connector_put(connector);
+
+	return ret;
+}
+DEFINE_SHOW_ATTRIBUTE(scdc_status);
+
+/**
+ * drm_scdc_debugfs_init - Initialize scdc files in connector debugfs
+ * @connector: pointer to &struct drm_connector to operate on
+ * @root: debugfs &struct dentry for the debugfs root of @connector
+ *
+ * Creates SCDC-related debugfs files for @connector. Must be called after
+ * @root is already created.
+ */
+void drm_scdc_debugfs_init(struct drm_connector *connector, struct dentry *root)
+{
+	if (!root || !connector)
+		return;
+
+	debugfs_create_file("scdc_status", 0444, root, connector, &scdc_status_fops);
+}
+EXPORT_SYMBOL(drm_scdc_debugfs_init);
diff --git a/include/drm/display/drm_scdc_helper.h b/include/drm/display/drm_scdc_helper.h
index e9ccaeba56dd..e0b79d79e1ff 100644
--- a/include/drm/display/drm_scdc_helper.h
+++ b/include/drm/display/drm_scdc_helper.h
@@ -30,6 +30,34 @@
 
 struct drm_connector;
 struct i2c_adapter;
+struct dentry;
+
+struct drm_scdc_status_flags {
+	/* Status Register 0 */
+	bool clock_detected;
+	bool ch0_locked;
+	bool ch1_locked;
+	bool ch2_locked;
+};
+
+struct drm_scdc_state {
+	/** @stf: contents of the status flag registers */
+	struct drm_scdc_status_flags stf;
+	/** @scramling_enabled: true if TMDS scrambling is on */
+	bool scrambling_enabled;
+	/** @scrambling_detected: true if the sink actually detected scrambling */
+	bool scrambling_detected;
+	/**
+	 * @tmds_bclk_x40: true if TMDS bit period is 1/40th of the TMDS
+	 * clock period, false if it's 1/10th of the clock period.
+	 */
+	bool tmds_bclk_x40;
+	/** @error_count: character error counts for each channel */
+	u16 error_count[3];
+
+	/** @scdc: raw SCDC data buffer */
+	u8 scdc[256];
+};
 
 int drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
 		  size_t size);
@@ -77,4 +105,8 @@ bool drm_scdc_get_scrambling_status(struct drm_connector *connector);
 bool drm_scdc_set_scrambling(struct drm_connector *connector, bool enable);
 bool drm_scdc_set_high_tmds_clock_ratio(struct drm_connector *connector, bool set);
 
+int drm_scdc_read_state(struct drm_connector *connector,
+			struct drm_scdc_state *state);
+void drm_scdc_debugfs_init(struct drm_connector *connector, struct dentry *root);
+
 #endif

-- 
2.55.0

[PATCH v9 3/5] drm/scdc-helper: Implement parsing and printing HDMI 2.1 fields

[Nicolas Frattaroli]

HDMI 2.1 redefines previously reserved fields in SCDC for various new
uses. No version check needs to be performed, as an HDMI 2.0 sink's
reserved SCDC fields are well-defined to be 0, and any zero-ness of
these fields for an HDMI 2.0 sink is not a surprise for SCDC parsers for
HDMI 2.1.

Implement reading and outputting these fields over debugfs.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/display/drm_scdc_helper.c | 103 ++++++++++++++++++++++++++++--
 include/drm/display/drm_scdc.h            |  21 +++++-
 include/drm/display/drm_scdc_helper.h     |  69 +++++++++++++++++++-
 3 files changed, 185 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c b/drivers/gpu/drm/display/drm_scdc_helper.c
index 129a2b85527b..d00da20862fc 100644
--- a/drivers/gpu/drm/display/drm_scdc_helper.c
+++ b/drivers/gpu/drm/display/drm_scdc_helper.c
@@ -21,6 +21,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/bitfield.h>
 #include <linux/export.h>
 #include <linux/i2c.h>
 #include <linux/slab.h>
@@ -57,6 +58,38 @@
 
 #define SCDC_I2C_SLAVE_ADDRESS 0x54
 
+static const char *drm_scdc_frl_rate_str(enum drm_scdc_frl_rate rate)
+{
+	switch (rate) {
+	case SCDC_FRL_RATE_OFF:
+		return "Off";
+	case SCDC_FRL_RATE_3X3:
+		return "3 Gbit/s x 3 lanes";
+	case SCDC_FRL_RATE_6X3:
+		return "6 Gbit/s x 3 lanes";
+	case SCDC_FRL_RATE_6X4:
+		return "6 Gbit/s x 4 lanes";
+	case SCDC_FRL_RATE_8X4:
+		return "8 Gbit/s x 4 lanes";
+	case SCDC_FRL_RATE_10X4:
+		return "10 Gbit/s x 4 lanes";
+	case SCDC_FRL_RATE_12X4:
+		return "12 Gbit/s x 4 lanes";
+	case SCDC_FRL_RATE_RESV_7:
+	case SCDC_FRL_RATE_RESV_8:
+	case SCDC_FRL_RATE_RESV_9:
+	case SCDC_FRL_RATE_RESV_10:
+	case SCDC_FRL_RATE_RESV_11:
+	case SCDC_FRL_RATE_RESV_12:
+	case SCDC_FRL_RATE_RESV_13:
+	case SCDC_FRL_RATE_RESV_14:
+	case SCDC_FRL_RATE_RESV_15:
+		return "(Reserved)";
+	default:
+		return NULL;
+	}
+}
+
 /**
  * drm_scdc_read - read a block of data from SCDC
  * @adapter: I2C controller
@@ -286,14 +319,41 @@ drm_scdc_parse_status0_flags(u8 val, struct drm_scdc_status_flags *flags)
 	flags->ch0_locked = val & SCDC_CH0_LOCK;
 	flags->ch1_locked = val & SCDC_CH1_LOCK;
 	flags->ch2_locked = val & SCDC_CH2_LOCK;
+	flags->ln3_locked = val & SCDC_LN3_LOCK;
+	flags->flt_ready = val & SCDC_FLT_READY;
+	flags->dsc_fail = val & SCDC_DSC_FAIL;
+}
+
+static void
+drm_scdc_parse_status1_2_flags(u8 val_flag1, u8 val_flag2,
+			       struct drm_scdc_status_flags *flags)
+{
+	flags->ln0_training_pattern = FIELD_GET(SCDC_LN_EVEN_TRAIN_PTRN, val_flag1);
+	flags->ln1_training_pattern = FIELD_GET(SCDC_LN_ODD_TRAIN_PTRN, val_flag1);
+
+	flags->ln2_training_pattern = FIELD_GET(SCDC_LN_EVEN_TRAIN_PTRN, val_flag2);
+	flags->ln3_training_pattern = FIELD_GET(SCDC_LN_ODD_TRAIN_PTRN, val_flag2);
 }
 
-static int drm_scdc_parse_error_counters(const u8 scdc[256], u16 counter[3])
+static int drm_scdc_parse_error_counters(const u8 scdc[256], u16 counter[4],
+					 unsigned int num_lanes)
 {
+	u8 end_reg;
 	u8 sum = 0;
 	int i;
 
-	for (i = SCDC_ERR_DET_0_L; i <= SCDC_ERR_DET_CHECKSUM ; i++)
+	switch (num_lanes) {
+	case 3:
+		end_reg = SCDC_ERR_DET_CHECKSUM;
+		break;
+	case 4:
+		end_reg = SCDC_ERR_DET_3_H;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	for (i = SCDC_ERR_DET_0_L; i <= end_reg; i++)
 		sum = wrapping_add(u8, sum, scdc[i]);
 
 	if (sum)
@@ -308,6 +368,12 @@ static int drm_scdc_parse_error_counters(const u8 scdc[256], u16 counter[3])
 			counter[i] = 0;
 	}
 
+	if (num_lanes == 4 && scdc[SCDC_ERR_DET_3_H] & SCDC_CHANNEL_VALID)
+		counter[3] =  (scdc[SCDC_ERR_DET_3_H] & ~SCDC_CHANNEL_VALID) << 8 |
+			      scdc[SCDC_ERR_DET_3_L];
+	else
+		counter[3] = 0;
+
 	return 0;
 }
 
@@ -325,6 +391,7 @@ int drm_scdc_read_state(struct drm_connector *connector, struct drm_scdc_state *
 	struct i2c_adapter *ddc;
 	struct drm_scdc *scdc;
 	u8 *buf = state->scdc;
+	int num_lanes;
 	int ret;
 
 	if (!state || !connector)
@@ -350,11 +417,26 @@ int drm_scdc_read_state(struct drm_connector *connector, struct drm_scdc_state *
 
 	state->scrambling_detected = buf[SCDC_SCRAMBLER_STATUS] & SCDC_SCRAMBLING_STATUS;
 
+	state->rate = FIELD_GET(SCDC_FRL_RATE, buf[SCDC_CONFIG_1]);
+	num_lanes = drm_scdc_num_frl_lanes(state->rate);
+	if (num_lanes < 0)
+		return num_lanes;
+	if (!num_lanes)
+		num_lanes = 3;
+
+	state->ffe_levels = FIELD_GET(SCDC_FFE_LEVELS, buf[SCDC_CONFIG_1]);
+
 	drm_scdc_parse_status0_flags(buf[SCDC_STATUS_FLAGS_0], &state->stf);
-	ret = drm_scdc_parse_error_counters(buf, state->error_count);
+	drm_scdc_parse_status1_2_flags(buf[SCDC_STATUS_FLAGS_1],
+				       buf[SCDC_STATUS_FLAGS_2], &state->stf);
+	ret = drm_scdc_parse_error_counters(buf, state->error_count, num_lanes);
 	if (ret)
 		return ret;
 
+	if (state->rate && (buf[SCDC_ERR_DET_RS_H] & SCDC_CHANNEL_VALID))
+		state->rs_corrections = (buf[SCDC_ERR_DET_RS_H] & ~SCDC_CHANNEL_VALID) << 8 |
+					buf[SCDC_ERR_DET_RS_L];
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_scdc_read_state);
@@ -371,7 +453,7 @@ static int scdc_status_show(struct seq_file *m, void *data)
 	struct drm_connector *connector = m->private;
 	struct drm_scdc *scdc = &connector->display_info.hdmi.scdc;
 	struct drm_scdc_state *st;
-	int i, ret;
+	int i, ret, frl_lanes;
 
 	drm_connector_get(connector);
 
@@ -414,8 +496,12 @@ static int scdc_status_show(struct seq_file *m, void *data)
 
 	drm_connector_put(connector);
 
+	frl_lanes = drm_scdc_num_frl_lanes(st->rate);
+
 	scdc_print_flag(m, "Scrambling Enabled", st->scrambling_enabled);
 	scdc_print_flag(m, "Scrambling Detected", st->scrambling_detected);
+	scdc_print_str(m, "FRL Rate", drm_scdc_frl_rate_str(st->rate));
+	scdc_print_dec(m, "FFE Levels", st->ffe_levels);
 
 	if (st->tmds_bclk_x40)
 		scdc_print_str(m, "TMDS Bit Clock Ratio", "1/40");
@@ -426,10 +512,19 @@ static int scdc_status_show(struct seq_file *m, void *data)
 	scdc_print_flag(m, "Channel 0 Locked", st->stf.ch0_locked);
 	scdc_print_flag(m, "Channel 1 Locked", st->stf.ch1_locked);
 	scdc_print_flag(m, "Channel 2 Locked", st->stf.ch2_locked);
+	if (frl_lanes == 4)
+		scdc_print_flag(m, "Lane 3 Locked", st->stf.ln3_locked);
+
+	scdc_print_flag(m, "Sink Ready For Link Training", st->stf.flt_ready);
+	scdc_print_flag(m, "Sink Failed To Decode DSC", st->stf.dsc_fail);
 
 	scdc_print_dec(m, "Channel 0 Errors", st->error_count[0]);
 	scdc_print_dec(m, "Channel 1 Errors", st->error_count[1]);
 	scdc_print_dec(m, "Channel 2 Errors", st->error_count[2]);
+	if (frl_lanes == 4)
+		scdc_print_dec(m, "Lane 3 Errors", st->error_count[3]);
+	if (frl_lanes > 0)
+		scdc_print_dec(m, "Reed-Solomon Corrections", st->rs_corrections);
 
 	kfree(st);
 
diff --git a/include/drm/display/drm_scdc.h b/include/drm/display/drm_scdc.h
index 3d58f37e8ed8..7f0b05b2f280 100644
--- a/include/drm/display/drm_scdc.h
+++ b/include/drm/display/drm_scdc.h
@@ -29,6 +29,8 @@
 #define SCDC_SOURCE_VERSION 0x02
 
 #define SCDC_UPDATE_0 0x10
+#define  SCDC_RSED_UPDATE (1 << 6)
+#define  SCDC_FLT_UPDATE (1 << 5)
 #define  SCDC_READ_REQUEST_TEST (1 << 2)
 #define  SCDC_CED_UPDATE (1 << 1)
 #define  SCDC_STATUS_UPDATE (1 << 0)
@@ -46,14 +48,25 @@
 #define SCDC_CONFIG_0 0x30
 #define  SCDC_READ_REQUEST_ENABLE (1 << 0)
 
+#define SCDC_CONFIG_1 0x31
+#define  SCDC_FRL_RATE   0x0f
+#define  SCDC_FFE_LEVELS 0xf0
+
 #define SCDC_STATUS_FLAGS_0 0x40
+#define  SCDC_DSC_FAIL (1 << 7)
+#define  SCDC_FLT_READY (1 << 6)
+#define  SCDC_LN3_LOCK (1 << 4)
 #define  SCDC_CH2_LOCK (1 << 3)
 #define  SCDC_CH1_LOCK (1 << 2)
 #define  SCDC_CH0_LOCK (1 << 1)
-#define  SCDC_CH_LOCK_MASK (SCDC_CH2_LOCK | SCDC_CH1_LOCK | SCDC_CH0_LOCK)
+#define  SCDC_CH_LOCK_MASK (SCDC_LN3_LOCK | SCDC_CH2_LOCK | SCDC_CH1_LOCK | \
+			    SCDC_CH0_LOCK)
 #define  SCDC_CLOCK_DETECT (1 << 0)
 
 #define SCDC_STATUS_FLAGS_1 0x41
+#define  SCDC_LN_EVEN_TRAIN_PTRN 0x0f
+#define  SCDC_LN_ODD_TRAIN_PTRN 0xf0
+#define SCDC_STATUS_FLAGS_2 0x42
 
 #define SCDC_ERR_DET_0_L 0x50
 #define SCDC_ERR_DET_0_H 0x51
@@ -65,6 +78,12 @@
 
 #define SCDC_ERR_DET_CHECKSUM 0x56
 
+#define SCDC_ERR_DET_3_L 0x57
+#define SCDC_ERR_DET_3_H 0x58
+
+#define SCDC_ERR_DET_RS_L 0x59
+#define SCDC_ERR_DET_RS_H 0x5a
+
 #define SCDC_TEST_CONFIG_0 0xc0
 #define  SCDC_TEST_READ_REQUEST (1 << 7)
 #define  SCDC_TEST_READ_REQUEST_DELAY(x) ((x) & 0x7f)
diff --git a/include/drm/display/drm_scdc_helper.h b/include/drm/display/drm_scdc_helper.h
index e0b79d79e1ff..a3b20adaac7e 100644
--- a/include/drm/display/drm_scdc_helper.h
+++ b/include/drm/display/drm_scdc_helper.h
@@ -24,6 +24,7 @@
 #ifndef DRM_SCDC_HELPER_H
 #define DRM_SCDC_HELPER_H
 
+#include <linux/errno.h>
 #include <linux/types.h>
 
 #include <drm/display/drm_scdc.h>
@@ -38,8 +39,65 @@ struct drm_scdc_status_flags {
 	bool ch0_locked;
 	bool ch1_locked;
 	bool ch2_locked;
+	bool ln3_locked;
+	bool flt_ready;
+	bool dsc_fail;
+
+	/* Status Register 1 */
+	u8 ln0_training_pattern : 4;
+	u8 ln1_training_pattern : 4;
+
+	/* Status Register 2 */
+	u8 ln2_training_pattern : 4;
+	u8 ln3_training_pattern : 4;
+};
+
+enum drm_scdc_frl_rate {
+	SCDC_FRL_RATE_OFF = 0,
+	SCDC_FRL_RATE_3X3 = 1,
+	SCDC_FRL_RATE_6X3 = 2,
+	SCDC_FRL_RATE_6X4 = 3,
+	SCDC_FRL_RATE_8X4 = 4,
+	SCDC_FRL_RATE_10X4 = 5,
+	SCDC_FRL_RATE_12X4 = 6,
+	SCDC_FRL_RATE_RESV_7 = 7,
+	SCDC_FRL_RATE_RESV_8 = 8,
+	SCDC_FRL_RATE_RESV_9 = 9,
+	SCDC_FRL_RATE_RESV_10 = 10,
+	SCDC_FRL_RATE_RESV_11 = 11,
+	SCDC_FRL_RATE_RESV_12 = 12,
+	SCDC_FRL_RATE_RESV_13 = 13,
+	SCDC_FRL_RATE_RESV_14 = 14,
+	SCDC_FRL_RATE_RESV_15 = 15
 };
 
+/**
+ * drm_scdc_num_frl_lanes - get number of lanes for a given FRL rate
+ * @rate: one of &enum drm_scdc_frl_rate
+ *
+ * For a given @rate, return the number of lanes it uses.
+ *
+ * Returns: %-EINVAL if @rate is not a valid FRL rate, or the number of lanes
+ * for a given &enum drm_scdc_frl_rate on success (including %0 for "off")
+ */
+static inline __pure int drm_scdc_num_frl_lanes(enum drm_scdc_frl_rate rate)
+{
+	switch (rate) {
+	case SCDC_FRL_RATE_OFF:
+		return 0;
+	case SCDC_FRL_RATE_3X3:
+	case SCDC_FRL_RATE_6X3:
+		return 3;
+	case SCDC_FRL_RATE_6X4:
+	case SCDC_FRL_RATE_8X4:
+	case SCDC_FRL_RATE_10X4:
+	case SCDC_FRL_RATE_12X4:
+		return 4;
+	default:
+		return -EINVAL;
+	}
+}
+
 struct drm_scdc_state {
 	/** @stf: contents of the status flag registers */
 	struct drm_scdc_status_flags stf;
@@ -52,9 +110,14 @@ struct drm_scdc_state {
 	 * clock period, false if it's 1/10th of the clock period.
 	 */
 	bool tmds_bclk_x40;
-	/** @error_count: character error counts for each channel */
-	u16 error_count[3];
-
+	/** @rate: FRL rate set by the source */
+	enum drm_scdc_frl_rate rate : 4;
+	/** @ffe_levels: The FFE levels for @rate set by the source */
+	u8 ffe_levels : 4;
+	/** @error_count: character error counts for each channel/link */
+	u16 error_count[4];
+	/** @rs_corrections: number of Reed-Solomon Corrections */
+	u16 rs_corrections;
 	/** @scdc: raw SCDC data buffer */
 	u8 scdc[256];
 };

-- 
2.55.0

[PATCH v9 4/5] drm/debugfs: Move HDMI debugfs registration to state helper

[Nicolas Frattaroli]

The HDMI debugfs files are only useful for connectors that already make
use of the HDMI state helpers. In addition, relying on HDMI-specific
functions in drm_debugfs.c can lead to circular linking problems later
down the line.

Move hdmi_debugfs_add() and friends to a new helper in
drm_hdmi_state_helper.c, and make all current users (vc4, sun4i, bridge)
either use it as a debugfs_init func, or call it directly in its
debugfs_init func.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/display/drm_bridge_connector.c  |   3 +
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 154 +++++++++++++++++++++++
 drivers/gpu/drm/drm_debugfs.c                   | 157 ------------------------
 drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c          |   1 +
 drivers/gpu/drm/vc4/vc4_hdmi.c                  |   1 +
 include/drm/display/drm_hdmi_state_helper.h     |   3 +
 6 files changed, 162 insertions(+), 157 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index 8b54069fa53a..00feb73e63d7 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -263,6 +263,9 @@ static void drm_bridge_connector_debugfs_init(struct drm_connector *connector,
 		if (bridge->funcs->debugfs_init)
 			bridge->funcs->debugfs_init(bridge, root);
 	}
+
+	if (bridge_connector->bridge_hdmi)
+		drm_hdmi_connector_debugfs_init(connector, root);
 }
 
 static struct drm_connector_state *
diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index ce17eeefc2da..8d5ee10ceb87 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: MIT
 
+#include <linux/debugfs.h>
 #include <linux/export.h>
 
 #include <drm/drm_atomic.h>
@@ -965,6 +966,159 @@ drm_hdmi_connector_mode_valid(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_hdmi_connector_mode_valid);
 
+static ssize_t
+audio_infoframe_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos)
+{
+	struct drm_connector_hdmi_infoframe *infoframe;
+	struct drm_connector *connector;
+	union hdmi_infoframe *frame;
+	u8 buf[HDMI_INFOFRAME_SIZE(AUDIO)];
+	ssize_t len = 0;
+
+	connector = filp->private_data;
+	mutex_lock(&connector->hdmi.infoframes.lock);
+
+	infoframe = &connector->hdmi.infoframes.audio;
+	if (!infoframe->set)
+		goto out;
+
+	frame = &infoframe->data;
+	len = hdmi_infoframe_pack(frame, buf, sizeof(buf));
+	if (len < 0)
+		goto out;
+
+	len = simple_read_from_buffer(ubuf, count, ppos, buf, len);
+
+out:
+	mutex_unlock(&connector->hdmi.infoframes.lock);
+	return len;
+}
+
+static const struct file_operations audio_infoframe_fops = {
+	.owner   = THIS_MODULE,
+	.open    = simple_open,
+	.read    = audio_infoframe_read,
+};
+
+static int create_hdmi_audio_infoframe_file(struct drm_connector *connector,
+					    struct dentry *parent)
+{
+	struct dentry *file;
+
+	if (!connector->hdmi.funcs ||
+	    !connector->hdmi.funcs->audio.write_infoframe)
+		return 0;
+
+	file = debugfs_create_file("audio", 0400, parent, connector, &audio_infoframe_fops);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	return 0;
+}
+
+#define DEFINE_INFOFRAME_FILE(_f) \
+static ssize_t _f##_read_infoframe(struct file *filp, \
+				   char __user *ubuf, \
+				   size_t count,      \
+				   loff_t *ppos)      \
+{ \
+	struct drm_connector_hdmi_infoframe *infoframe; \
+	struct drm_connector_state *conn_state; \
+	struct drm_connector *connector; \
+	union hdmi_infoframe *frame; \
+	struct drm_device *dev; \
+	u8 buf[HDMI_INFOFRAME_SIZE(MAX)]; \
+	ssize_t len = 0; \
+	\
+	connector = filp->private_data; \
+	dev = connector->dev; \
+	\
+	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL); \
+	\
+	conn_state = connector->state; \
+	infoframe = &conn_state->hdmi.infoframes._f; \
+	if (!infoframe->set) \
+		goto out; \
+	\
+	frame = &infoframe->data; \
+	len = hdmi_infoframe_pack(frame, buf, sizeof(buf)); \
+	if (len < 0) \
+		goto out; \
+	\
+	len = simple_read_from_buffer(ubuf, count, ppos, buf, len); \
+	\
+out: \
+	drm_modeset_unlock(&dev->mode_config.connection_mutex); \
+	return len; \
+} \
+\
+static const struct file_operations _f##_infoframe_fops = { \
+	.owner = THIS_MODULE, \
+	.open = simple_open, \
+	.read = _f##_read_infoframe, \
+}; \
+\
+static int create_hdmi_## _f ## _infoframe_file(struct drm_connector *connector, \
+						struct dentry *parent) \
+{ \
+	struct dentry *file; \
+	\
+	if (!connector->hdmi.funcs || \
+	    !connector->hdmi.funcs->_f.write_infoframe) \
+		return 0; \
+	file = debugfs_create_file(#_f, 0400, parent, connector, &_f ## _infoframe_fops); \
+	if (IS_ERR(file)) \
+		return PTR_ERR(file); \
+	\
+	return 0; \
+}
+
+DEFINE_INFOFRAME_FILE(avi);
+DEFINE_INFOFRAME_FILE(hdmi);
+DEFINE_INFOFRAME_FILE(hdr_drm);
+DEFINE_INFOFRAME_FILE(spd);
+
+static int create_hdmi_infoframe_files(struct drm_connector *connector,
+				       struct dentry *parent)
+{
+	int ret;
+
+	ret = create_hdmi_audio_infoframe_file(connector, parent);
+	if (ret)
+		return ret;
+
+	ret = create_hdmi_avi_infoframe_file(connector, parent);
+	if (ret)
+		return ret;
+
+	ret = create_hdmi_hdmi_infoframe_file(connector, parent);
+	if (ret)
+		return ret;
+
+	ret = create_hdmi_hdr_drm_infoframe_file(connector, parent);
+	if (ret)
+		return ret;
+
+	ret = create_hdmi_spd_infoframe_file(connector, parent);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+void drm_hdmi_connector_debugfs_init(struct drm_connector *connector,
+				     struct dentry *root)
+{
+	struct dentry *dir;
+
+	dir = debugfs_create_dir("infoframes", root);
+	if (IS_ERR(dir))
+		return;
+
+	create_hdmi_infoframe_files(connector, dir);
+}
+EXPORT_SYMBOL(drm_hdmi_connector_debugfs_init);
+
 static int clear_infoframe(struct drm_connector *connector,
 			   const struct drm_connector_infoframe_funcs *funcs,
 			   const char *type)
diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index ae1c6126c2c5..a72f9723d3a9 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -633,161 +633,6 @@ static const struct file_operations drm_connector_fops = {
 	.write = connector_write
 };
 
-static ssize_t
-audio_infoframe_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos)
-{
-	struct drm_connector_hdmi_infoframe *infoframe;
-	struct drm_connector *connector;
-	union hdmi_infoframe *frame;
-	u8 buf[HDMI_INFOFRAME_SIZE(AUDIO)];
-	ssize_t len = 0;
-
-	connector = filp->private_data;
-	mutex_lock(&connector->hdmi.infoframes.lock);
-
-	infoframe = &connector->hdmi.infoframes.audio;
-	if (!infoframe->set)
-		goto out;
-
-	frame = &infoframe->data;
-	len = hdmi_infoframe_pack(frame, buf, sizeof(buf));
-	if (len < 0)
-		goto out;
-
-	len = simple_read_from_buffer(ubuf, count, ppos, buf, len);
-
-out:
-	mutex_unlock(&connector->hdmi.infoframes.lock);
-	return len;
-}
-
-static const struct file_operations audio_infoframe_fops = {
-	.owner   = THIS_MODULE,
-	.open    = simple_open,
-	.read    = audio_infoframe_read,
-};
-
-static int create_hdmi_audio_infoframe_file(struct drm_connector *connector,
-					    struct dentry *parent)
-{
-	struct dentry *file;
-
-	if (!connector->hdmi.funcs ||
-	    !connector->hdmi.funcs->audio.write_infoframe)
-		return 0;
-
-	file = debugfs_create_file("audio", 0400, parent, connector, &audio_infoframe_fops);
-	if (IS_ERR(file))
-		return PTR_ERR(file);
-
-	return 0;
-}
-
-#define DEFINE_INFOFRAME_FILE(_f) \
-static ssize_t _f##_read_infoframe(struct file *filp, \
-				   char __user *ubuf, \
-				   size_t count,      \
-				   loff_t *ppos)      \
-{ \
-	struct drm_connector_hdmi_infoframe *infoframe; \
-	struct drm_connector_state *conn_state; \
-	struct drm_connector *connector; \
-	union hdmi_infoframe *frame; \
-	struct drm_device *dev; \
-	u8 buf[HDMI_INFOFRAME_SIZE(MAX)]; \
-	ssize_t len = 0; \
-	\
-	connector = filp->private_data; \
-	dev = connector->dev; \
-	\
-	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL); \
-	\
-	conn_state = connector->state; \
-	infoframe = &conn_state->hdmi.infoframes._f; \
-	if (!infoframe->set) \
-		goto out; \
-	\
-	frame = &infoframe->data; \
-	len = hdmi_infoframe_pack(frame, buf, sizeof(buf)); \
-	if (len < 0) \
-		goto out; \
-	\
-	len = simple_read_from_buffer(ubuf, count, ppos, buf, len); \
-	\
-out: \
-	drm_modeset_unlock(&dev->mode_config.connection_mutex); \
-	return len; \
-} \
-\
-static const struct file_operations _f##_infoframe_fops = { \
-	.owner = THIS_MODULE, \
-	.open = simple_open, \
-	.read = _f##_read_infoframe, \
-}; \
-\
-static int create_hdmi_## _f ## _infoframe_file(struct drm_connector *connector, \
-						struct dentry *parent) \
-{ \
-	struct dentry *file; \
-	\
-	if (!connector->hdmi.funcs || \
-	    !connector->hdmi.funcs->_f.write_infoframe) \
-		return 0; \
-	file = debugfs_create_file(#_f, 0400, parent, connector, &_f ## _infoframe_fops); \
-	if (IS_ERR(file)) \
-		return PTR_ERR(file); \
-	\
-	return 0; \
-}
-
-DEFINE_INFOFRAME_FILE(avi);
-DEFINE_INFOFRAME_FILE(hdmi);
-DEFINE_INFOFRAME_FILE(hdr_drm);
-DEFINE_INFOFRAME_FILE(spd);
-
-static int create_hdmi_infoframe_files(struct drm_connector *connector,
-				       struct dentry *parent)
-{
-	int ret;
-
-	ret = create_hdmi_audio_infoframe_file(connector, parent);
-	if (ret)
-		return ret;
-
-	ret = create_hdmi_avi_infoframe_file(connector, parent);
-	if (ret)
-		return ret;
-
-	ret = create_hdmi_hdmi_infoframe_file(connector, parent);
-	if (ret)
-		return ret;
-
-	ret = create_hdmi_hdr_drm_infoframe_file(connector, parent);
-	if (ret)
-		return ret;
-
-	ret = create_hdmi_spd_infoframe_file(connector, parent);
-	if (ret)
-		return ret;
-
-	return 0;
-}
-
-static void hdmi_debugfs_add(struct drm_connector *connector)
-{
-	struct dentry *dir;
-
-	if (!(connector->connector_type == DRM_MODE_CONNECTOR_HDMIA ||
-	      connector->connector_type == DRM_MODE_CONNECTOR_HDMIB))
-		return;
-
-	dir = debugfs_create_dir("infoframes", connector->debugfs_entry);
-	if (IS_ERR(dir))
-		return;
-
-	create_hdmi_infoframe_files(connector, dir);
-}
-
 void drm_debugfs_connector_add(struct drm_connector *connector)
 {
 	struct drm_device *dev = connector->dev;
@@ -815,8 +660,6 @@ void drm_debugfs_connector_add(struct drm_connector *connector)
 	debugfs_create_file("output_bpc", 0444, root, connector,
 			    &output_bpc_fops);
 
-	hdmi_debugfs_add(connector);
-
 	if (connector->funcs->debugfs_init)
 		connector->funcs->debugfs_init(connector, root);
 }
diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
index e99f52ebb26f..e6c4f121ad0c 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
@@ -292,6 +292,7 @@ static void sun4i_hdmi_connector_reset(struct drm_connector *connector)
 }
 
 static const struct drm_connector_funcs sun4i_hdmi_connector_funcs = {
+	.debugfs_init		= drm_hdmi_connector_debugfs_init,
 	.detect			= sun4i_hdmi_connector_detect,
 	.fill_modes		= drm_helper_probe_single_connector_modes,
 	.reset			= sun4i_hdmi_connector_reset,
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 17c8635c5afa..ea1f2013b20e 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -513,6 +513,7 @@ static void vc4_hdmi_connector_reset(struct drm_connector *connector)
 }
 
 static const struct drm_connector_funcs vc4_hdmi_connector_funcs = {
+	.debugfs_init = drm_hdmi_connector_debugfs_init,
 	.force = drm_atomic_helper_connector_hdmi_force,
 	.fill_modes = drm_helper_probe_single_connector_modes,
 	.reset = vc4_hdmi_connector_reset,
diff --git a/include/drm/display/drm_hdmi_state_helper.h b/include/drm/display/drm_hdmi_state_helper.h
index 13375bd0f4ae..596c57d9d250 100644
--- a/include/drm/display/drm_hdmi_state_helper.h
+++ b/include/drm/display/drm_hdmi_state_helper.h
@@ -3,6 +3,7 @@
 #ifndef DRM_HDMI_STATE_HELPER_H_
 #define DRM_HDMI_STATE_HELPER_H_
 
+struct dentry;
 struct drm_atomic_commit;
 struct drm_connector;
 struct drm_connector_state;
@@ -29,5 +30,7 @@ void drm_atomic_helper_connector_hdmi_force(struct drm_connector *connector);
 enum drm_mode_status
 drm_hdmi_connector_mode_valid(struct drm_connector *connector,
 			      const struct drm_display_mode *mode);
+void drm_hdmi_connector_debugfs_init(struct drm_connector *connector,
+				     struct dentry *root);
 
 #endif // DRM_HDMI_STATE_HELPER_H_

-- 
2.55.0

[PATCH v9 5/5] drm/display: hdmi-state-helper: Init SCDC debugfs for HDMI

[Nicolas Frattaroli]

Initialise the SCDC debugfs file for connectors that call the HDMI state
helper's debugfs_init helper. This makes all connectors that use the
helper expose the scdc_status file in their connector debugfs.

Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index 8d5ee10ceb87..709524b40c26 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -13,6 +13,7 @@
 #include <drm/display/drm_hdmi_cec_helper.h>
 #include <drm/display/drm_hdmi_helper.h>
 #include <drm/display/drm_hdmi_state_helper.h>
+#include <drm/display/drm_scdc_helper.h>
 
 /**
  * DOC: hdmi helpers
@@ -1116,6 +1117,7 @@ void drm_hdmi_connector_debugfs_init(struct drm_connector *connector,
 		return;
 
 	create_hdmi_infoframe_files(connector, dir);
+	drm_scdc_debugfs_init(connector, root);
 }
 EXPORT_SYMBOL(drm_hdmi_connector_debugfs_init);
 

-- 
2.55.0

Re: [PATCH v9 0/5] Add SCDC information to connector debugfs

[Jani Nikula]

On Fri, 24 Jul 2026, Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:
> HDMI uses the DDC I2C bus for communicating various bits of link status
> out of band with the actual HDMI video signal. This information can be
> useful for debugging issues like questionable cables sabotaged by feline
> teeth, Enthusiast Grade cables made of cow fencing wire, and other such
> problems that ruin one's media viewing plans.
>
> Consequently, this series exposes various bits of pertinent information
> from the SCDC protocol in an HDMI connector's debugfs. To continually
> poll the link status, userspace can poll the debugfs file.

Is there a reason we can't add a character device node for this similar
to DP AUX? See config DRM_DISPLAY_DP_AUX_CHARDEV.

It's ultimately more generic than deciphering everything in kernel.


BR,
Jani.





>
> ---
> Changes in v9:
> - Unlock mode_config.mutex on disconnected connector early exit
> - Calculate and print Reed-Solomon error corrections counter on != 4
>   lane FRL as well. Technically a functional change to an already
>   reviewed patch, but I kept the R-b because it's so minor.
> - Link to v8: https://patch.msgid.link/20260722-scdc-link-health-v8-0-cd1dacbb85d9@collabora.com
>
> Changes in v8:
> - Acquire mode_config mutex in an interruptible way during
>   scdc_status_show to avoid racing connector state
> - Remove scdc_debugfs_priv, use connector as debugfs entry priv instead
> - Allocate and free state in scdc_status_show, since it doesn't need to
>   persist across debugfs reads
> - Check for NULL ddc in drm_scdc_read_state in the unlikely event an
>   EDID with the SCDC flag was forced on a connector with no DDC
> - Note: drm_connector_get() is omitted from drm_scdc_debugfs_init
>   because drm_scdc_debugfs_init is called on connector construction and
>   the debugfs is removed on connector destruction. Adding a redundant
>   reference increase here would necessitate introducing a destruction
>   callback to mirror the debugfs_init connector op for the sole purpose
>   of decreasing the counter again.
> - Link to v7: https://patch.msgid.link/20260721-scdc-link-health-v7-0-92df1b6ad5fc@collabora.com
>
> Changes in v7:
> - Move HDMI debugfs registration to new state helper, fix up all users
>   (sun4i, vc4, bridge)
> - Register scdc debugfs in new hdmi debugfs helper
> - Link to v6: https://patch.msgid.link/20260611-scdc-link-health-v6-0-6307875a6b5e@collabora.com
>
> Changes in v6:
> - Fix off-by-one error in drm_scdc_read_state
> - Link to v5: https://patch.msgid.link/20260604-scdc-link-health-v5-0-11173b0ac3de@collabora.com
>
> Changes in v5:
> - Read all SCDC data regardless of update flags
> - Dump SCDC data as hex before the human-readable output. It's separated
>   with "\n----------------\n\n".
> - No longer write 0 to read-only registers
> - Add Reed-Solomon Corrections counter parsing
> - Parsing has been kept. A desire was expressed to get this data without
>   any external userspace tooling, and the kernel will need to parse it
>   eventually anyway to set the link status.
> - Functions have been made static as of right now, since external users
>   may do another pass over the function signatures anyway.
> - Link to v4: https://patch.msgid.link/20260527-scdc-link-health-v4-0-622ea40a1f59@collabora.com
>
> Changes in v4:
> - Don't use C struct bitfields for parsing status flags. Switch to
>   bitwise AND for boolean flags, and FIELD_GET for multi-bit values.
> - Drop the superfluous !! and parens
> - Drop the __pure attributes on static functions
> - Initialise stack local arrays with {}, not { 0 }.
> - I've kept the print macros and %-30s format. Reason being that I don't
>   want to repeat the format specifier and str_yes_no(foo) a bunch, and I
>   like the %-30s format because it means all values are aligned with the
>   value of the longest field, which is 30 chars long.
> - Link to v3: https://patch.msgid.link/20260526-scdc-link-health-v3-0-59e4a4aaead1@collabora.com
>
> Changes in v3:
> - Add patch to change return type of drm_scdc_read/write.
> - Rework error counter reading to duplicate less code.
> - Also check lane 3 counter valid flag when reading its error counter.
> - Use memset to clear buf for error counters, rather than doing it in
>   the loop.
> - Make read_error_counters not accept 0 as num_lanes; fix it up in the
>   caller instead.
> - Link to v2: https://patch.msgid.link/20260520-scdc-link-health-v2-0-511af18cd64b@collabora.com
>
> Changes in v2:
> - Add HDMI 2.1 SCDC status reporting
> - Link to v1: https://patch.msgid.link/20260415-scdc-link-health-v1-0-8e731e88eaf0@collabora.com
>
> To: Jani Nikula <jani.nikula@linux.intel.com>
> To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> To: Maxime Ripard <mripard@kernel.org>
> To: Thomas Zimmermann <tzimmermann@suse.de>
> To: David Airlie <airlied@gmail.com>
> To: Simona Vetter <simona@ffwll.ch>
> To: Andrzej Hajda <andrzej.hajda@intel.com>
> To: Neil Armstrong <neil.armstrong@linaro.org>
> To: Robert Foss <rfoss@kernel.org>
> To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> To: Jonas Karlman <jonas@kwiboo.se>
> To: Jernej Skrabec <jernej.skrabec@gmail.com>
> To: Luca Ceresoli <luca.ceresoli@bootlin.com>
> To: Daniel Stone <daniel@fooishbar.org>
> To: Hans Verkuil <hverkuil+cisco@kernel.org>
> To: Chen-Yu Tsai <wens@kernel.org>
> To: Samuel Holland <samuel@sholland.org>
> To: Dave Stevenson <dave.stevenson@raspberrypi.com>
> To: Maíra Canal <mcanal@igalia.com>
> To: Raspberry Pi Kernel Maintenance <kernel-list@raspberrypi.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kernel@collabora.com
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-sunxi@lists.linux.dev
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
>
> ---
> Nicolas Frattaroli (5):
>       drm/scdc-helper: Don't use ssize_t return type for scdc_read/write
>       drm/scdc-helper: Add scdc_status debugfs entry
>       drm/scdc-helper: Implement parsing and printing HDMI 2.1 fields
>       drm/debugfs: Move HDMI debugfs registration to state helper
>       drm/display: hdmi-state-helper: Init SCDC debugfs for HDMI
>
>  drivers/gpu/drm/display/drm_bridge_connector.c  |   3 +
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 156 +++++++++++++
>  drivers/gpu/drm/display/drm_scdc_helper.c       | 289 +++++++++++++++++++++++-
>  drivers/gpu/drm/drm_debugfs.c                   | 157 -------------
>  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c          |   1 +
>  drivers/gpu/drm/vc4/vc4_hdmi.c                  |   1 +
>  include/drm/display/drm_hdmi_state_helper.h     |   3 +
>  include/drm/display/drm_scdc.h                  |  21 +-
>  include/drm/display/drm_scdc_helper.h           | 103 ++++++++-
>  9 files changed, 568 insertions(+), 166 deletions(-)
> ---
> base-commit: b747a63003130bef1a3d5d6ba97c94d0cee36f55
> change-id: 20260413-scdc-link-health-89326013d96c
>
> Best regards,
> --  
> Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
>

-- 
Jani Nikula, Intel

Re: [PATCH v9 0/5] Add SCDC information to connector debugfs

[Nicolas Frattaroli]

On Monday, 27 July 2026 10:35:15 Central European Summer Time Jani Nikula wrote:
> On Fri, 24 Jul 2026, Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:
> > HDMI uses the DDC I2C bus for communicating various bits of link status
> > out of band with the actual HDMI video signal. This information can be
> > useful for debugging issues like questionable cables sabotaged by feline
> > teeth, Enthusiast Grade cables made of cow fencing wire, and other such
> > problems that ruin one's media viewing plans.
> >
> > Consequently, this series exposes various bits of pertinent information
> > from the SCDC protocol in an HDMI connector's debugfs. To continually
> > poll the link status, userspace can poll the debugfs file.
> 
> Is there a reason we can't add a character device node for this similar
> to DP AUX? See config DRM_DISPLAY_DP_AUX_CHARDEV.

You already can just point tools at the ddc symlink to the i2c dev.

The idea here is to be able to read this out of debugfs without
any additional external tooling needed.

> It's ultimately more generic than deciphering everything in kernel.

The kernel will need to decipher this in the future anyway for HDMI 2.x
support, including so that it can set link status to bad when there's a
glut of errors.

> 
> 
> BR,
> Jani.
> 
> 
> 
> 
> 
> >
> > ---
> > Changes in v9:
> > - Unlock mode_config.mutex on disconnected connector early exit
> > - Calculate and print Reed-Solomon error corrections counter on != 4
> >   lane FRL as well. Technically a functional change to an already
> >   reviewed patch, but I kept the R-b because it's so minor.
> > - Link to v8: https://patch.msgid.link/20260722-scdc-link-health-v8-0-cd1dacbb85d9@collabora.com
> >
> > Changes in v8:
> > - Acquire mode_config mutex in an interruptible way during
> >   scdc_status_show to avoid racing connector state
> > - Remove scdc_debugfs_priv, use connector as debugfs entry priv instead
> > - Allocate and free state in scdc_status_show, since it doesn't need to
> >   persist across debugfs reads
> > - Check for NULL ddc in drm_scdc_read_state in the unlikely event an
> >   EDID with the SCDC flag was forced on a connector with no DDC
> > - Note: drm_connector_get() is omitted from drm_scdc_debugfs_init
> >   because drm_scdc_debugfs_init is called on connector construction and
> >   the debugfs is removed on connector destruction. Adding a redundant
> >   reference increase here would necessitate introducing a destruction
> >   callback to mirror the debugfs_init connector op for the sole purpose
> >   of decreasing the counter again.
> > - Link to v7: https://patch.msgid.link/20260721-scdc-link-health-v7-0-92df1b6ad5fc@collabora.com
> >
> > Changes in v7:
> > - Move HDMI debugfs registration to new state helper, fix up all users
> >   (sun4i, vc4, bridge)
> > - Register scdc debugfs in new hdmi debugfs helper
> > - Link to v6: https://patch.msgid.link/20260611-scdc-link-health-v6-0-6307875a6b5e@collabora.com
> >
> > Changes in v6:
> > - Fix off-by-one error in drm_scdc_read_state
> > - Link to v5: https://patch.msgid.link/20260604-scdc-link-health-v5-0-11173b0ac3de@collabora.com
> >
> > Changes in v5:
> > - Read all SCDC data regardless of update flags
> > - Dump SCDC data as hex before the human-readable output. It's separated
> >   with "\n----------------\n\n".
> > - No longer write 0 to read-only registers
> > - Add Reed-Solomon Corrections counter parsing
> > - Parsing has been kept. A desire was expressed to get this data without
> >   any external userspace tooling, and the kernel will need to parse it
> >   eventually anyway to set the link status.
> > - Functions have been made static as of right now, since external users
> >   may do another pass over the function signatures anyway.
> > - Link to v4: https://patch.msgid.link/20260527-scdc-link-health-v4-0-622ea40a1f59@collabora.com
> >
> > Changes in v4:
> > - Don't use C struct bitfields for parsing status flags. Switch to
> >   bitwise AND for boolean flags, and FIELD_GET for multi-bit values.
> > - Drop the superfluous !! and parens
> > - Drop the __pure attributes on static functions
> > - Initialise stack local arrays with {}, not { 0 }.
> > - I've kept the print macros and %-30s format. Reason being that I don't
> >   want to repeat the format specifier and str_yes_no(foo) a bunch, and I
> >   like the %-30s format because it means all values are aligned with the
> >   value of the longest field, which is 30 chars long.
> > - Link to v3: https://patch.msgid.link/20260526-scdc-link-health-v3-0-59e4a4aaead1@collabora.com
> >
> > Changes in v3:
> > - Add patch to change return type of drm_scdc_read/write.
> > - Rework error counter reading to duplicate less code.
> > - Also check lane 3 counter valid flag when reading its error counter.
> > - Use memset to clear buf for error counters, rather than doing it in
> >   the loop.
> > - Make read_error_counters not accept 0 as num_lanes; fix it up in the
> >   caller instead.
> > - Link to v2: https://patch.msgid.link/20260520-scdc-link-health-v2-0-511af18cd64b@collabora.com
> >
> > Changes in v2:
> > - Add HDMI 2.1 SCDC status reporting
> > - Link to v1: https://patch.msgid.link/20260415-scdc-link-health-v1-0-8e731e88eaf0@collabora.com
> >
> > To: Jani Nikula <jani.nikula@linux.intel.com>
> > To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > To: Maxime Ripard <mripard@kernel.org>
> > To: Thomas Zimmermann <tzimmermann@suse.de>
> > To: David Airlie <airlied@gmail.com>
> > To: Simona Vetter <simona@ffwll.ch>
> > To: Andrzej Hajda <andrzej.hajda@intel.com>
> > To: Neil Armstrong <neil.armstrong@linaro.org>
> > To: Robert Foss <rfoss@kernel.org>
> > To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> > To: Jonas Karlman <jonas@kwiboo.se>
> > To: Jernej Skrabec <jernej.skrabec@gmail.com>
> > To: Luca Ceresoli <luca.ceresoli@bootlin.com>
> > To: Daniel Stone <daniel@fooishbar.org>
> > To: Hans Verkuil <hverkuil+cisco@kernel.org>
> > To: Chen-Yu Tsai <wens@kernel.org>
> > To: Samuel Holland <samuel@sholland.org>
> > To: Dave Stevenson <dave.stevenson@raspberrypi.com>
> > To: Maíra Canal <mcanal@igalia.com>
> > To: Raspberry Pi Kernel Maintenance <kernel-list@raspberrypi.com>
> > Cc: dri-devel@lists.freedesktop.org
> > Cc: linux-kernel@vger.kernel.org
> > Cc: kernel@collabora.com
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-sunxi@lists.linux.dev
> > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> >
> > ---
> > Nicolas Frattaroli (5):
> >       drm/scdc-helper: Don't use ssize_t return type for scdc_read/write
> >       drm/scdc-helper: Add scdc_status debugfs entry
> >       drm/scdc-helper: Implement parsing and printing HDMI 2.1 fields
> >       drm/debugfs: Move HDMI debugfs registration to state helper
> >       drm/display: hdmi-state-helper: Init SCDC debugfs for HDMI
> >
> >  drivers/gpu/drm/display/drm_bridge_connector.c  |   3 +
> >  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 156 +++++++++++++
> >  drivers/gpu/drm/display/drm_scdc_helper.c       | 289 +++++++++++++++++++++++-
> >  drivers/gpu/drm/drm_debugfs.c                   | 157 -------------
> >  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c          |   1 +
> >  drivers/gpu/drm/vc4/vc4_hdmi.c                  |   1 +
> >  include/drm/display/drm_hdmi_state_helper.h     |   3 +
> >  include/drm/display/drm_scdc.h                  |  21 +-
> >  include/drm/display/drm_scdc_helper.h           | 103 ++++++++-
> >  9 files changed, 568 insertions(+), 166 deletions(-)
> > ---
> > base-commit: b747a63003130bef1a3d5d6ba97c94d0cee36f55
> > change-id: 20260413-scdc-link-health-89326013d96c
> >
> > Best regards,
> > --  
> > Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> >
> 
>