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 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>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel@collabora.com
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
Nicolas Frattaroli (4):
drm/scdc-helper: Don't use ssize_t return type for scdc_read/write
drm/scdc-helper: Add scdc_status debugfs entry
drm/display: bridge_connector: init scdc debugfs for HDMI
drm/scdc-helper: Implement parsing and printing HDMI 2.1 fields
drivers/gpu/drm/display/drm_bridge_connector.c | 4 +
drivers/gpu/drm/display/drm_scdc_helper.c | 285 ++++++++++++++++++++++++-
include/drm/display/drm_scdc.h | 21 +-
include/drm/display/drm_scdc_helper.h | 103 ++++++++-
4 files changed, 404 insertions(+), 9 deletions(-)
---
base-commit: 9dd27c9ba89acc30350aa57fe047b9a2fd0a5ee7
change-id: 20260413-scdc-link-health-89326013d96c
Best regards,
--
Nicolas Frattaroli <nicolas.frattaroli@collabora.com>