Re: [PATCH v1] i2c: designware: amdisp: Fix null pointer dereference in runtime resume
From: Mario Limonciello
Date: Fri Mar 20 2026 - 10:03:28 EST
On 3/19/2026 4:09 PM, Nirujogi, Pratap wrote:
Hi Mario,Good investigation. Since this was around all the time and just got worse I would say you should add a fixes tag for the first commit that introduced this driver rather than 38fa29b01a6a295aedb69d1bbdad70acd7d204c6 and just note in the commit message that 38fa29b01a6a295aedb69d1bbdad70acd7d204c6 made it worse.
On 3/9/2026 9:29 PM, Mario Limonciello wrote:
My apologies for mixing up this change along with other changes that were needed to fix the AMD ISP driver regressions in v7.0.
On 3/9/2026 5:00 PM, Pratap Nirujogi wrote:
Add NULL check for i_dev->map before calling i2c_dw_init() in the
runtime resume path. The regmap may not be initialized yet when
runtime PM tries to resume the device early in the probe sequence,
leading to a NULL pointer dereference. Skip the i2c_dw_init() call
if regmap is not yet created.
This race condition occurs when runtime PM resume is triggered before
i2c_dw_probe() completes the regmap initialization and was observed in
kernel v7.0 where the order of device enumeration has changed because
of the changes in registering the device sources in the device hierarchy.
Co-developed-by: Bin Du <Bin.Du@xxxxxxx>
Fixes: 02c057ddefef ("ACPI: video: Convert the driver to a platform one")
Is this the right commit that introduced the race? Did it change the timing?
Or was the race always there and we just got lucky until that commit went in?
I investigated further and found that this issue was exposed by the below commit.
https://github.com/torvalds/linux/ commit/38fa29b01a6a295aedb69d1bbdad70acd7d204c6
However, the resume‑probe race condition existed even earlier and had not surfaced because device initialization in resume is done only when init handle is valid.
Here is some background and context on this change:
The amdisp i2c device requires ISP to be in power on state for probe to succeed. To meet this requirement, we added this device, which is a amdgpu MFD child to the genpd, to control isp power using runtime PM. The pm_runtime_get_sync() call before probe triggers a PM resume, which powers on the ISP and also invokes the amdisp i2c runtime resume before the probe completes resulting in this race condition.
To fix this issue properly, I’m considering this change. Please review and share your feedback on whether this makes sense.
- Call dev_pm_genpd_resume() to Power ON ISP before probe
- Call dev_pm_genpd_suspend() to Power OFF ISP after probe
- Call pm_runtime_enable() after probe is successful to take care of system suspend/resume.
diff --git a/drivers/i2c/busses/i2c-designware-amdisp.c b/drivers/i2c/ busses/i2c-designware-amdisp.c
index 19de518be30a4..9ce58522951cd 100644
--- a/drivers/i2c/busses/i2c-designware-amdisp.c
+++ b/drivers/i2c/busses/i2c-designware-amdisp.c
@@ -7,6 +7,7 @@
#include <linux/module.h>
#include <linux/platform_device.h>
+#include <linux/pm_domain.h>
#include <linux/pm_runtime.h>
#include <linux/soc/amd/isp4_misc.h>
@@ -76,9 +77,7 @@ static int amd_isp_dw_i2c_plat_probe(struct platform_device *pdev)
device_enable_async_suspend(&pdev->dev);
- pm_runtime_enable(&pdev->dev);
- pm_runtime_get_sync(&pdev->dev);
-
+ dev_pm_genpd_resume(&pdev->dev);
ret = i2c_dw_probe(isp_i2c_dev);
if (ret) {
@@ -86,14 +85,14 @@ static int amd_isp_dw_i2c_plat_probe(struct platform_device *pdev)
goto error_release_rpm;
}
-
- pm_runtime_put_sync(&pdev->dev);
+ dev_pm_genpd_suspend(&pdev->dev);
+ pm_runtime_set_suspended(&pdev->dev);
+ pm_runtime_enable(&pdev->dev);
return 0;
error_release_rpm:
amd_isp_dw_i2c_plat_pm_cleanup(isp_i2c_dev);
- pm_runtime_put_sync(&pdev->dev);
return ret;
}