[PATCH v6 2/7] phy: qcom: qmp-usbc: Prevent unnecessary PM runtime suspend at boot

[Loic Poulain]

Runtime PM has to be enabled before creating the PHYs, since phy_create()
only enables runtime PM on the PHY devices if it is already enabled on
this parent device. This opens a small window where the device can be
runtime suspended after pm_runtime_enable() and before the later
pm_runtime_forbid(), causing an unnecessary suspend/resume cycle while
the PHYs are not yet registered.

Take a runtime PM usage reference with pm_runtime_get_noresume() before
enabling runtime PM and release it once the PHYs have been created to
prevent the device from being runtime suspended during that window.

This also makes the probe path safe independently of pm_runtime_forbid(),
which is a good preparation for potentially dropping the forbid() call in
the future and letting runtime PM be enabled by default.

Reviewed-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
Reviewed-by: Abel Vesa <abel.vesa@xxxxxxxxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
Signed-off-by: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>
---
 drivers/phy/qualcomm/phy-qcom-qmp-usbc.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usbc.c b/drivers/phy/qualcomm/phy-qcom-qmp-usbc.c
index ab3055bb5b0c198832ae06dfcd04fd34395e271d..780a6b4f71eb41adf8f7011db8676c56f704b933 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-usbc.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-usbc.c
@@ -1959,10 +1959,16 @@ static int qmp_usbc_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_node_put;
 
+	/*
+	 * Enable runtime PM before creating the PHYs, phy_create() only enables
+	 * it on the PHY devices if already enabled on the parent. Hold a usage
+	 * reference so callbacks cannot run until the PHY is ready.
+	 */
+	pm_runtime_get_noresume(dev);
 	pm_runtime_set_active(dev);
 	ret = devm_pm_runtime_enable(dev);
 	if (ret)
-		goto err_node_put;
+		goto err_pm_put;
 	/*
 	 * Prevent runtime pm from being ON by default. Users can enable
 	 * it using power/control in sysfs.
@@ -1971,13 +1977,13 @@ static int qmp_usbc_probe(struct platform_device *pdev)
 
 	ret = qmp_usbc_register_clocks(qmp, np);
 	if (ret)
-		goto err_node_put;
+		goto err_pm_put;
 
 	qmp->usb_phy = devm_phy_create(dev, np, &qmp_usbc_usb_phy_ops);
 	if (IS_ERR(qmp->usb_phy)) {
 		ret = PTR_ERR(qmp->usb_phy);
 		dev_err(dev, "failed to create PHY: %d\n", ret);
-		goto err_node_put;
+		goto err_pm_put;
 	}
 
 	phy_set_drvdata(qmp->usb_phy, qmp);
@@ -1987,17 +1993,25 @@ static int qmp_usbc_probe(struct platform_device *pdev)
 		if (IS_ERR(qmp->dp_phy)) {
 			ret = PTR_ERR(qmp->dp_phy);
 			dev_err(dev, "failed to create PHY: %d\n", ret);
-			goto err_node_put;
+			goto err_pm_put;
 		}
 		phy_set_drvdata(qmp->dp_phy, qmp);
 	}
 
+	phy_provider = devm_of_phy_provider_register(dev, qmp_usbc_phy_xlate);
+	if (IS_ERR(phy_provider)) {
+		ret = PTR_ERR(phy_provider);
+		goto err_pm_put;
+	}
+
 	of_node_put(np);
 
-	phy_provider = devm_of_phy_provider_register(dev, qmp_usbc_phy_xlate);
+	pm_runtime_put(dev);
 
-	return PTR_ERR_OR_ZERO(phy_provider);
+	return 0;
 
+err_pm_put:
+	pm_runtime_put_noidle(dev);
 err_node_put:
 	of_node_put(np);
 	return ret;

-- 
2.34.1