[PATCH V3 RFC 8/9] usb: dwc2: Implement recovery after PM domain off

[Stefan Wahren <wahrenst@gmx.net>]

According to the dt-bindings there are some platforms, which have a
dedicated USB power domain for DWC2 IP core supply. If the power domain
is switched off during system suspend then all USB register will lose
their settings.

Use GUSBCFG_TOUTCAL as a canary to detect that the power domain has
been powered off during suspend. Since the GOTGCTL_CURMODE_HOST doesn't
match on all platform with the current mode, additionally backup
GINTSTS. This works reliable to decide which registers should be
restored.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
---
 drivers/usb/dwc2/core.c     |  1 +
 drivers/usb/dwc2/core.h     |  2 ++
 drivers/usb/dwc2/platform.c | 38 +++++++++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

Hi, would be nice to get some feedback about the approach and
test results on other DWC2 platforms.

diff --git a/drivers/usb/dwc2/core.c b/drivers/usb/dwc2/core.c
index 9919ab725d54..c3d24312db0f 100644
--- a/drivers/usb/dwc2/core.c
+++ b/drivers/usb/dwc2/core.c
@@ -43,6 +43,7 @@ int dwc2_backup_global_registers(struct dwc2_hsotg *hsotg)
 	/* Backup global regs */
 	gr = &hsotg->gr_backup;

+	gr->gintsts = dwc2_readl(hsotg, GINTSTS);
 	gr->gotgctl = dwc2_readl(hsotg, GOTGCTL);
 	gr->gintmsk = dwc2_readl(hsotg, GINTMSK);
 	gr->gahbcfg = dwc2_readl(hsotg, GAHBCFG);
diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
index 81e8632f29ed..e65a74853bb0 100644
--- a/drivers/usb/dwc2/core.h
+++ b/drivers/usb/dwc2/core.h
@@ -667,6 +667,7 @@ struct dwc2_hw_params {
 /**
  * struct dwc2_gregs_backup - Holds global registers state before
  * entering partial power down
+ * @gintsts:		Backup of GINTSTS register
  * @gotgctl:		Backup of GOTGCTL register
  * @gintmsk:		Backup of GINTMSK register
  * @gahbcfg:		Backup of GAHBCFG register
@@ -683,6 +684,7 @@ struct dwc2_hw_params {
  * @valid:		True if registers values backuped.
  */
 struct dwc2_gregs_backup {
+	u32 gintsts;
 	u32 gotgctl;
 	u32 gintmsk;
 	u32 gahbcfg;
diff --git a/drivers/usb/dwc2/platform.c b/drivers/usb/dwc2/platform.c
index 7b84416dfc2b..39e9064b6cfe 100644
--- a/drivers/usb/dwc2/platform.c
+++ b/drivers/usb/dwc2/platform.c
@@ -683,6 +683,14 @@ static int __maybe_unused dwc2_suspend(struct device *dev)
 		regulator_disable(dwc2->usb33d);
 	}

+	if (is_device_mode)
+		ret = dwc2_gadget_backup_critical_registers(dwc2);
+	else
+		ret = dwc2_host_backup_critical_registers(dwc2);
+
+	if (ret)
+		return ret;
+
 	if (dwc2->ll_hw_enabled &&
 	    (is_device_mode || dwc2_host_can_poweroff_phy(dwc2))) {
 		ret = __dwc2_lowlevel_hw_disable(dwc2);
@@ -692,6 +700,24 @@ static int __maybe_unused dwc2_suspend(struct device *dev)
 	return ret;
 }

+static int dwc2_restore_critical_registers(struct dwc2_hsotg *hsotg)
+{
+	struct dwc2_gregs_backup *gr;
+
+	gr = &hsotg->gr_backup;
+
+	if (!gr->valid) {
+		dev_err(hsotg->dev, "%s: no registers to restore\n",
+			__func__);
+		return -EINVAL;
+	}
+
+	if (gr->gintsts & GINTSTS_CURMODE_HOST)
+		return dwc2_host_restore_critical_registers(hsotg);
+
+	return dwc2_gadget_restore_critical_registers(hsotg);
+}
+
 static int __maybe_unused dwc2_resume(struct device *dev)
 {
 	struct dwc2_hsotg *dwc2 = dev_get_drvdata(dev);
@@ -704,6 +730,18 @@ static int __maybe_unused dwc2_resume(struct device *dev)
 	}
 	dwc2->phy_off_for_suspend = false;

+	/*
+	 * During suspend it's possible that the power domain for the
+	 * DWC2 controller is disabled and all register values get lost.
+	 * In case the GUSBCFG register is not initialized, it's clear the
+	 * registers must be restored.
+	 */
+	if (!(dwc2_readl(dwc2, GUSBCFG) & GUSBCFG_TOUTCAL_MASK)) {
+		ret = dwc2_restore_critical_registers(dwc2);
+		if (ret)
+			return ret;
+	}
+
 	if (dwc2->params.activate_stm_id_vb_detection) {
 		unsigned long flags;
 		u32 ggpio, gotgctl;
--
2.34.1