[PATCH v3] phy: qcom-qusb2: Fix NULL pointer dereference on early suspend

[Loic Poulain]

Enabling runtime PM before attaching the QPHY instance as driver data
can lead to a NULL pointer dereference in runtime PM callbacks that
expect valid driver data. There is a small window where the suspend
callback may run after PM runtime enabling and before runtime forbid.
This causes a sporadic crash during boot:

```
Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a1
[...]
CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 6.16.7+ #116 PREEMPT
Workqueue: pm pm_runtime_work
pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : qusb2_phy_runtime_suspend+0x14/0x1e0 [phy_qcom_qusb2]
lr : pm_generic_runtime_suspend+0x2c/0x44
[...]
```

Attach the QPHY instance as driver data before enabling runtime PM to
prevent NULL pointer dereference in runtime PM callbacks.

Reorder pm_runtime_enable() and pm_runtime_forbid() to prevent a
short window where an unnecessary runtime suspend can occur.

Use the devres-managed version to ensure PM runtime is symmetrically
disabled during driver removal for proper cleanup.

Fixes: 891a96f65ac3 ("phy: qcom-qusb2: Add support for runtime PM")
Signed-off-by: Loic Poulain <loic.poulain at oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at oss.qualcomm.com>
---
 v3: The phy-core expects parent's runtime-pm to be setup before creating
     the phy, so move back runtime-pm to its initial location and
     relocate dev_set_drvdata() instead.

 v2: Move runtime-pm enabling after dev_set_drvdata
     use devm_pm_runtime_enable() to fix unbalanced enabling on removal
     reword commit message

 drivers/phy/qualcomm/phy-qcom-qusb2.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qusb2.c b/drivers/phy/qualcomm/phy-qcom-qusb2.c
index b5514a32ff8f..6386d834b0e4 100644
--- a/drivers/phy/qualcomm/phy-qcom-qusb2.c
+++ b/drivers/phy/qualcomm/phy-qcom-qusb2.c
@@ -1093,29 +1093,27 @@ static int qusb2_phy_probe(struct platform_device *pdev)
 		or->hsdisc_trim.override = true;
 	}
 
-	pm_runtime_set_active(dev);
-	pm_runtime_enable(dev);
+	dev_set_drvdata(dev, qphy);
+
 	/*
-	 * Prevent runtime pm from being ON by default. Users can enable
-	 * it using power/control in sysfs.
+	 * Enable runtime PM support, but forbid it by default.
+	 * Users can allow it again via the power/control attribute in sysfs.
 	 */
+	pm_runtime_set_active(dev);
 	pm_runtime_forbid(dev);
+	devm_pm_runtime_enable(dev);
 
 	generic_phy = devm_phy_create(dev, NULL, &qusb2_phy_gen_ops);
 	if (IS_ERR(generic_phy)) {
 		ret = PTR_ERR(generic_phy);
 		dev_err(dev, "failed to create phy, %d\n", ret);
-		pm_runtime_disable(dev);
 		return ret;
 	}
 	qphy->phy = generic_phy;
 
-	dev_set_drvdata(dev, qphy);
 	phy_set_drvdata(generic_phy, qphy);
 
 	phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
-	if (IS_ERR(phy_provider))
-		pm_runtime_disable(dev);
 
 	return PTR_ERR_OR_ZERO(phy_provider);
 }
-- 
2.34.1