From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87A9A33C732; Sun, 1 Jun 2025 23:45:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748821555; cv=none; b=kCXV6gOy8tMMuNKOzRKTPkgyDTvCE5URsXS3zNJjVZqfxcfydKpXIxrPVIPNIHJKpIB5TXVNp4AfonQOku7V6BYIJcJkOP0bY8xikxIV38zAR+3VUoBsRbXZyISlYwB3zIeuZTPtq6LUo4BPdjoBy6Tj7FHSxAFIOTOSM20ZGFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748821555; c=relaxed/simple; bh=kUGwDRq+MjUiyxVnJChfdYbnrlb+IJMC0fgD+z+UX7I=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=qUUdBHzIdx8PNyzT4cYeYKSsUtjPlL1DiFUfvNg29cyCFBSObUv7hRJ9J8xq1rcoapFuyhXYdY0BFqJ4VNf6eYf716Y54aTWw88hTY0Rcdembw3muIuBRWJ8GtNZ7cOD7iNxz9APWZyfPDLcgno2wDRpUqwiPhBwZrGTvvo8/Zc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=f1CbMcfs; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="f1CbMcfs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F652C4CEE7; Sun, 1 Jun 2025 23:45:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748821554; bh=kUGwDRq+MjUiyxVnJChfdYbnrlb+IJMC0fgD+z+UX7I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=f1CbMcfsTObBM9COWIyxdj7DzUKgOESZFohfr+yMM60a6gbXvl5lBsr213LoXWTA1 LhEfQ+fi0Np7L79HaQiOpZp6Abd7G3TQPZe1QTbjCyXN3dPKkKFR4yNTDtrvYIAWDS M3ASALb8d/lRw66SauV8aUd6utFvcJubO7DVSD30nA321cs2tIYJHtzLKm0ajRsaDe Js5la4O02fOsjNR4ZZbLtO1bEkgijocgUPxcatQkZsdGSlk1yokE8yEO8jeekncajc NBRBpfLTMmNMz17pNjOU7tjfBDyOMtq+KIXdcxlIK9FfIl/hvWI4Zhd/BZcgqsVyKi OI7vqUaMiRizw== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Hans Verkuil , Maxime Ripard , Mauro Carvalho Chehab , Sasha Levin , mchehab@kernel.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH AUTOSEL 5.4 15/22] media: tc358743: ignore video while HPD is low Date: Sun, 1 Jun 2025 19:45:06 -0400 Message-Id: <20250601234515.3519309-15-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250601234515.3519309-1-sashal@kernel.org> References: <20250601234515.3519309-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.4.293 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Hans Verkuil [ 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 Tested-by: Maxime Ripard Link: https://lore.kernel.org/linux-media/20240628-stoic-bettong-of-fortitude-e25611@houat/ Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Sasha Levin --- **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 f042570bc5cae..f4ebe93a495c4 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; -- 2.39.5