[PATCH v5 4/5] phy: qcom: qmp-usb-legacy: Prevent unnecessary PM runtime suspend at boot

[Loic Poulain <loic.poulain@oss.qualcomm.com>]

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.

Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
index fc490589c8e4888770807a60170905a1c7610421..eb1826fb26f0868f7758245b0cbe1a0590fea9a3 100644
--- a/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
+++ b/drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c
@@ -1285,10 +1285,16 @@ static int qmp_usb_legacy_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.
@@ -1297,23 +1303,27 @@ static int qmp_usb_legacy_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_legacy_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);
 
+	pm_runtime_put(dev);
+
 	of_node_put(np);
 
 	phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
 
 	return PTR_ERR_OR_ZERO(phy_provider);
 
+err_pm_put:
+	pm_runtime_put_noidle(dev);
 err_node_put:
 	of_node_put(np);
 	return ret;

-- 
2.34.1