[PATCH 2/3] usb: dwc3: add reinit-phy-on-resume quirk

[Oliver White]

Some platforms gate the USB2 PHY power domain during deep sleep
(S3) even when device_may_wakeup is set, which causes the PHY
register state to be lost. The DWC3 fast resume path (taken when
device_may_wakeup is true) relies on phy_pm_runtime_get_sync() to
restore the PHY, but this is a no-op for PHY drivers that do not
implement runtime PM (e.g. the Qualcomm eUSB2 driver).

Add a new boolean quirk 'snps,reinit-phy-on-resume' that, when set,
forces a full phy_exit() + phy_init() cycle on each USB2 PHY during
the host-mode fast resume path. This ensures the PHY registers are
properly re-programmed after power loss.

Signed-off-by: Oliver White <oliverjwhite07@xxxxxxxxx>
---
 drivers/usb/dwc3/core.c | 25 +++++++++++++++++++++++++
 drivers/usb/dwc3/core.h |  1 +
 2 files changed, 26 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 161a4d58b2ce..82baaab0d1d1 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1854,6 +1854,8 @@ static void dwc3_get_properties(struct dwc3 *dwc)
 
 	dwc->dis_split_quirk = device_property_read_bool(dev,
 				"snps,dis-split-quirk");
+	dwc->reinit_phy_on_resume = device_property_read_bool(dev,
+				"snps,reinit-phy-on-resume");
 
 	dwc->lpm_nyet_threshold = lpm_nyet_threshold;
 	dwc->tx_de_emphasis = tx_de_emphasis;
@@ -2561,6 +2563,29 @@ static int dwc3_resume_common(struct dwc3 *dwc, pm_message_t msg)
 			dwc3_writel(dwc, DWC3_GUSB2PHYCFG(i), reg);
 		}
 
+		/*
+		 * Some platforms gate USB2 PHY power during deep sleep even
+		 * when device_may_wakeup is true, causing register state to be
+		 * lost.  Re-initialize the PHY to ensure clean signalling.
+		 */
+		if (dwc->reinit_phy_on_resume && !PMSG_IS_AUTO(msg)) {
+			for (i = 0; i < dwc->num_usb2_ports; i++) {
+				int ret;
+
+				ret = phy_exit(dwc->usb2_generic_phy[i]);
+				if (ret)
+					dev_warn_ratelimited(dwc->dev,
+						"failed to exit usb2 phy %d: %d\n",
+						i, ret);
+
+				ret = phy_init(dwc->usb2_generic_phy[i]);
+				if (ret)
+					dev_warn_ratelimited(dwc->dev,
+						"failed to init usb2 phy %d: %d\n",
+						i, ret);
+			}
+		}
+
 		for (i = 0; i < dwc->num_usb2_ports; i++)
 			phy_pm_runtime_get_sync(dwc->usb2_generic_phy[i]);
 		for (i = 0; i < dwc->num_usb3_ports; i++)
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index a35b3db1f9f3..f64cf709e194 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -1403,6 +1403,7 @@ struct dwc3 {
 	unsigned		dis_metastability_quirk:1;
 
 	unsigned		dis_split_quirk:1;
+	unsigned		reinit_phy_on_resume:1;
 	unsigned		async_callbacks:1;
 	unsigned		sys_wakeup:1;
 	unsigned		wakeup_configured:1;
-- 
2.53.0