linux-kernel - [PATCH AUTOSEL 6.14 027/102] drm/msm/hdmi: add runtime PM calls to DDC transfer function

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250601232937.3510379-27-sashal@kernel.org>
Date: Sun,  1 Jun 2025 19:28:19 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Jessica Zhang <quic_jesszhan@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	Sasha Levin <sashal@...nel.org>,
	robdclark@...il.com,
	quic_abhinavk@...cinc.com,
	lumag@...nel.org,
	airlied@...il.com,
	simona@...ll.ch,
	linux-arm-msm@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	freedreno@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 027/102] drm/msm/hdmi: add runtime PM calls to DDC transfer function

From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

[ Upstream commit 531b4e2c206e5f7dead04d9da84dfa693ac57481 ]

We must be sure that the HDMI controller is powered on, while performing
the DDC transfer. Add corresponding runtime PM calls to
msm_hdmi_i2c_xfer().

Reviewed-by: Jessica Zhang <quic_jesszhan@...cinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Patchwork: https://patchwork.freedesktop.org/patch/651727/
Link: https://lore.kernel.org/r/20250505-fd-hdmi-hpd-v5-8-48541f76318c@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---

**YES** This commit should be backported to stable kernel trees. Here's
my detailed analysis: ## Bug Fix Analysis This commit addresses a
**critical power management bug** in the MSM HDMI DDC (Display Data
Channel) implementation. The issue is that DDC transfers can occur when
the HDMI controller is not properly powered, leading to potential
hardware access failures or system instability. ## Code Changes Analysis
The changes in `drivers/gpu/drm/msm/hdmi/hdmi_i2c.c` are **minimal and
well-contained**: 1. **Added runtime PM calls around DDC operations**: -
`pm_runtime_resume_and_get()` at function start (line ~110) -
`pm_runtime_put()` in success path (line ~206) - `pm_runtime_put()` in
error path (line ~224) 2. **Fixed error handling flow**: - Changed
direct returns to proper `goto fail` to ensure PM put operations - Lines
113-114 and 172 now use `goto fail` instead of direct returns ## Risk
Assessment - LOW RISK **Minimal scope**: Only affects the
`msm_hdmi_i2c_xfer()` function, which is the DDC transfer entry point.
**Consistent with existing patterns**: The kernel tree analysis shows
runtime PM is already used extensively in this driver: -
`hdmi_bridge.c`: Uses `pm_runtime_get_sync()` and `pm_runtime_put()` -
`hdmi_hpd.c`: Uses runtime PM in 4 locations for HPD operations **No
architectural changes**: This follows the existing runtime PM pattern
established in commit 6ed9ed484d04 from 2017. ## Comparison with Similar
Commits This matches the characteristics of **Similar Commit #1**
(marked YES for backport): - Fixes a resource management bug (runtime PM
vs devres helper) - Small, contained change - Improves driver robustness
- Follows existing patterns The commit is **unlike** the rejected
commits (#2-#5) which were: - Code cleanups/refactoring - API
modernization - Feature additions - Non-critical improvements ##
Critical System Impact DDC is essential for HDMI functionality - it's
used for: - Reading display EDID data - Monitor detection - Display
capability negotiation Without proper power management, DDC operations
could fail intermittently, causing display detection issues or system
hangs when accessing unpowered hardware. ## Conclusion This is a **low-
risk, high-value bugfix** that ensures hardware is properly powered
during DDC operations. It follows established driver patterns, has
minimal scope, and fixes a potentially serious power management issue
that could affect display functionality.

 drivers/gpu/drm/msm/hdmi/hdmi_i2c.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/hdmi/hdmi_i2c.c b/drivers/gpu/drm/msm/hdmi/hdmi_i2c.c
index 7aa500d24240f..ebefea4fb4085 100644
--- a/drivers/gpu/drm/msm/hdmi/hdmi_i2c.c
+++ b/drivers/gpu/drm/msm/hdmi/hdmi_i2c.c
@@ -107,11 +107,15 @@ static int msm_hdmi_i2c_xfer(struct i2c_adapter *i2c,
 	if (num == 0)
 		return num;
 
+	ret = pm_runtime_resume_and_get(&hdmi->pdev->dev);
+	if (ret)
+		return ret;
+
 	init_ddc(hdmi_i2c);
 
 	ret = ddc_clear_irq(hdmi_i2c);
 	if (ret)
-		return ret;
+		goto fail;
 
 	for (i = 0; i < num; i++) {
 		struct i2c_msg *p = &msgs[i];
@@ -169,7 +173,7 @@ static int msm_hdmi_i2c_xfer(struct i2c_adapter *i2c,
 				hdmi_read(hdmi, REG_HDMI_DDC_SW_STATUS),
 				hdmi_read(hdmi, REG_HDMI_DDC_HW_STATUS),
 				hdmi_read(hdmi, REG_HDMI_DDC_INT_CTRL));
-		return ret;
+		goto fail;
 	}
 
 	ddc_status = hdmi_read(hdmi, REG_HDMI_DDC_SW_STATUS);
@@ -202,7 +206,13 @@ static int msm_hdmi_i2c_xfer(struct i2c_adapter *i2c,
 		}
 	}
 
+	pm_runtime_put(&hdmi->pdev->dev);
+
 	return i;
+
+fail:
+	pm_runtime_put(&hdmi->pdev->dev);
+	return ret;
 }
 
 static u32 msm_hdmi_i2c_func(struct i2c_adapter *adapter)
-- 
2.39.5