[PATCH v6 1/7] phy: qcom: qmp-combo: 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: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
Reviewed-by: Abel Vesa <abel.vesa@xxxxxxxxxxxxxxxx>
Reviewed-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
Signed-off-by: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>
---
 drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
index cdcfad2e86b1d37650c4d7b0433319837ee9c9d4..2cbe1d90662eebd5baf426dd9620cb5cc5d9256f 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
@@ -4934,10 +4934,16 @@ static int qmp_combo_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.
@@ -4946,14 +4952,13 @@ static int qmp_combo_probe(struct platform_device *pdev)
 
 	ret = qmp_combo_register_clocks(qmp, usb_np, dp_np);
 	if (ret)
-		goto err_node_put;
-
+		goto err_pm_put;
 
 	qmp->usb_phy = devm_phy_create(dev, usb_np, &qmp_combo_usb_phy_ops);
 	if (IS_ERR(qmp->usb_phy)) {
 		ret = PTR_ERR(qmp->usb_phy);
 		dev_err(dev, "failed to create USB PHY: %d\n", ret);
-		goto err_node_put;
+		goto err_pm_put;
 	}
 
 	phy_set_drvdata(qmp->usb_phy, qmp);
@@ -4962,7 +4967,7 @@ static int qmp_combo_probe(struct platform_device *pdev)
 	if (IS_ERR(qmp->dp_phy)) {
 		ret = PTR_ERR(qmp->dp_phy);
 		dev_err(dev, "failed to create DP PHY: %d\n", ret);
-		goto err_node_put;
+		goto err_pm_put;
 	}
 
 	phy_set_drvdata(qmp->dp_phy, qmp);
@@ -4972,11 +4977,20 @@ static int qmp_combo_probe(struct platform_device *pdev)
 	else
 		phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
 
+	if (IS_ERR(phy_provider)) {
+		ret = PTR_ERR(phy_provider);
+		goto err_pm_put;
+	}
+
 	of_node_put(usb_np);
 	of_node_put(dp_np);
 
-	return PTR_ERR_OR_ZERO(phy_provider);
+	pm_runtime_put(dev);
+
+	return 0;
 
+err_pm_put:
+	pm_runtime_put_noidle(dev);
 err_node_put:
 	of_node_put(usb_np);
 	of_node_put(dp_np);

-- 
2.34.1