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

[Loic Poulain]

Runtime PM has to be enabled before creating the PHY, since phy_create()
only enables runtime PM on the PHY device 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 PHY is not yet registered.

Take a runtime PM usage reference with pm_runtime_get_noresume() before
enabling runtime PM and release it once the PHY has 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.

Signed-off-by: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>
---
 drivers/phy/qualcomm/phy-qcom-qmp-usb.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usb.c b/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
index bb905c437a01e3b898b7259abe3e49df4756fc5b..b0790bcf0bc86459d0658ea1290888273c4ff391 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
@@ -2419,10 +2419,16 @@ static int qmp_usb_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_node_put;
 
+	/*
+	 * Enable runtime PM before creating the PHY, phy_create() only enables
+	 * it on the PHY device if already enabled on the parent. Hold a usage
+	 * reference so callbacks cannot run before qmp->phy is assigned.
+	 */
+	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.
@@ -2431,23 +2437,31 @@ static int qmp_usb_probe(struct platform_device *pdev)
 
 	ret = phy_pipe_clk_register(qmp, np);
 	if (ret)
-		goto err_node_put;
+		goto err_pm_put;
 
 	qmp->phy = devm_phy_create(dev, np, &qmp_usb_phy_ops);
 	if (IS_ERR(qmp->phy)) {
 		ret = PTR_ERR(qmp->phy);
 		dev_err(dev, "failed to create PHY: %d\n", ret);
-		goto err_node_put;
+		goto err_pm_put;
 	}
 
 	phy_set_drvdata(qmp->phy, qmp);
 
+	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(np);
 
-	phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_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