[PATCH 3/4] phy: qcom: qmp-usb-legacy: Fix possible NULL-deref on early runtime suspend

[Loic Poulain]

There is a small window where the runtime suspend callback may run
after pm_runtime_enable() and before pm_runtime_forbid(). In this
case, a crash occurs because runtime suspend/resume dereferences
qmp->phy pointer, which is not yet initialized:
        `if (!qmp->phy->init_count) {`

Similarly to other qcom phy drivers, introduce a qmp->phy_initialized
variable that can be used to avoid relying on the possibly uninitialized
phy pointer.

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

Fixes: e464a3180a43 ("phy: qcom-qmp-usb: split off the legacy USB+dp_com support")
Signed-off-by: Loic Poulain <loic.poulain at oss.qualcomm.com>
---
 .../phy/qualcomm/phy-qcom-qmp-usb-legacy.c    | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
index 8bf951b0490c..73439d223f1d 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
@@ -541,6 +541,7 @@ struct qmp_usb {
 	struct regulator_bulk_data *vregs;
 
 	enum phy_mode mode;
+	bool phy_initialized;
 
 	struct phy *phy;
 
@@ -895,6 +896,7 @@ static int qmp_usb_legacy_power_off(struct phy *phy)
 
 static int qmp_usb_legacy_enable(struct phy *phy)
 {
+	struct qmp_usb *qmp = phy_get_drvdata(phy);
 	int ret;
 
 	ret = qmp_usb_legacy_init(phy);
@@ -904,14 +906,19 @@ static int qmp_usb_legacy_enable(struct phy *phy)
 	ret = qmp_usb_legacy_power_on(phy);
 	if (ret)
 		qmp_usb_legacy_exit(phy);
+	else
+		qmp->phy_initialized = true;
 
 	return ret;
 }
 
 static int qmp_usb_legacy_disable(struct phy *phy)
 {
+	struct qmp_usb *qmp = phy_get_drvdata(phy);
 	int ret;
 
+	qmp->phy_initialized = false;
+
 	ret = qmp_usb_legacy_power_off(phy);
 	if (ret)
 		return ret;
@@ -988,7 +995,7 @@ static int __maybe_unused qmp_usb_legacy_runtime_suspend(struct device *dev)
 
 	dev_vdbg(dev, "Suspending QMP phy, mode:%d\n", qmp->mode);
 
-	if (!qmp->phy->init_count) {
+	if (!qmp->phy_initialized) {
 		dev_vdbg(dev, "PHY not initialized, bailing out\n");
 		return 0;
 	}
@@ -1009,7 +1016,7 @@ static int __maybe_unused qmp_usb_legacy_runtime_resume(struct device *dev)
 
 	dev_vdbg(dev, "Resuming QMP phy, mode:%d\n", qmp->mode);
 
-	if (!qmp->phy->init_count) {
+	if (!qmp->phy_initialized) {
 		dev_vdbg(dev, "PHY not initialized, bailing out\n");
 		return 0;
 	}
@@ -1277,15 +1284,15 @@ static int qmp_usb_legacy_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_node_put;
 
+	/*
+	 * 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);
 	ret = devm_pm_runtime_enable(dev);
 	if (ret)
 		goto err_node_put;
-	/*
-	 * Prevent runtime pm from being ON by default. Users can enable
-	 * it using power/control in sysfs.
-	 */
-	pm_runtime_forbid(dev);
 
 	ret = phy_pipe_clk_register(qmp, np);
 	if (ret)
-- 
2.34.1