From: Hans Verkuil hverkuil@xs4all.nl
[ Upstream commit 6829c5b5d26b1be31880d74ec24cb32d2d75f1ae ]
If the HPD is low (happens if there is no EDID or the EDID is being updated), then return -ENOLINK in tc358743_get_detected_timings() instead of detecting video.
This avoids userspace thinking that it can start streaming when the HPD is low.
Signed-off-by: Hans Verkuil hverkuil@xs4all.nl Tested-by: Maxime Ripard mripard@kernel.org Link: https://lore.kernel.org/linux-media/20240628-stoic-bettong-of-fortitude-e256... Signed-off-by: Mauro Carvalho Chehab mchehab+huawei@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Analysis of Code Changes The commit adds a simple but important HPD (Hot Plug Detect) check to the `tc358743_get_detected_timings()` function: ```c /bin /bin.usr-is-merged /boot /dev /etc /home /init /lib /lib.usr-is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var if HPD is low, ignore any video */ if (!(i2c_rd8(sd, HPD_CTL) & MASK_HPD_OUT0)) return -ENOLINK; ``` This 4-line addition is strategically placed **before** any video detection logic, creating an early exit when HPD is low. ## Why This Qualifies for Backporting ### 1. **Fixes Real User-Facing Bug** The commit addresses a genuine functional issue where the driver would incorrectly report video timings when no valid HDMI source was connected. This leads to: - Userspace applications attempting to stream when HPD is low - Resource waste and potential system instability - Poor user experience during cable connect/disconnect cycles ### 2. **Minimal and Contained Fix** - **Small scope**: Only 4 lines of code added - **Single function**: Only affects `tc358743_get_detected_timings()` - **Standard error handling**: Uses existing `-ENOLINK` return code - **No architectural changes**: Follows established driver patterns ### 3. **Low Regression Risk** - **Early return pattern**: Adds validation before existing logic - **Established error code**: `-ENOLINK` is already used elsewhere in the function - **No side effects**: Doesn't modify hardware state or driver data structures - **Conservative approach**: Only prevents false positives, doesn't change valid detection ### 4. **Quality Indicators** - **Expert authorship**: Hans Verkuil is a well-known V4L2 maintainer - **Proper testing**: Tested by Maxime Ripard, a significant kernel contributor - **Standard pattern**: Similar HPD checks exist in related HDMI bridge drivers - **Clear commit message**: Explains both the problem and solution ### 5. **Production Impact** - **Critical hardware**: tc358743 is used in production embedded systems (Raspberry Pi, industrial vision) - **Core functionality**: HDMI input capture is essential for these systems - **Embedded stability**: Stable kernels are crucial for embedded deployments ## Comparison to Reference Commits This commit aligns well with **Similar Commit #1** (backport status: YES), which also: - Fixed HPD-related detection logic - Made a small, contained change - Addressed user-facing functionality issues - Had minimal regression risk ## Technical Correctness The HPD check is technically sound: - **Hardware reality**: HPD low means no valid HDMI source is connected - **Logical placement**: Check occurs before expensive video detection - **Proper signaling**: `-ENOLINK` correctly indicates no link is available - **Resource efficiency**: Prevents unnecessary processing when no valid signal exists ## Stable Tree Criteria Met ✅ **Important bugfix**: Fixes streaming issues affecting end users ✅ **Small and contained**: 4-line addition with clear scope ✅ **Minimal risk**: Early return with existing error handling ✅ **No new features**: Pure bugfix without functional additions ✅ **Production relevance**: Affects systems in active deployment The commit represents exactly the type of targeted, low-risk fix that stable trees are designed to include - addressing real user issues without introducing architectural changes or significant regression risk.
drivers/media/i2c/tc358743.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/media/i2c/tc358743.c b/drivers/media/i2c/tc358743.c index 344a670e732fa..9b60ad3ce2590 100644 --- a/drivers/media/i2c/tc358743.c +++ b/drivers/media/i2c/tc358743.c @@ -309,6 +309,10 @@ static int tc358743_get_detected_timings(struct v4l2_subdev *sd,
memset(timings, 0, sizeof(struct v4l2_dv_timings));
+ /* if HPD is low, ignore any video */ + if (!(i2c_rd8(sd, HPD_CTL) & MASK_HPD_OUT0)) + return -ENOLINK; + if (no_signal(sd)) { v4l2_dbg(1, debug, sd, "%s: no valid signal\n", __func__); return -ENOLINK;