usb: dwc2: add support for host mode external vbus supply

This patch adds a way to enable an external vbus supply in host mode,
when dwc2 drvvbus signal is not used.

This patch is very similar to the one done in U-Boot dwc2 driver [1]. It
also adds dynamic vbus supply management depending on the role and state
of the core.

[1] https://lists.denx.de/pipermail/u-boot/2017-March/283434.htmlSigned-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc2/core.h

@@ -819,6 +819,7 @@ struct dwc2_hregs_backup {
  * @plat:               The platform specific configuration data. This can be
  *                      removed once all SoCs support usb transceiver.
  * @supplies:           Definition of USB power supplies
+ * @vbus_supply:        Regulator supplying vbus.
  * @phyif:              PHY interface width
  * @lock:		Spinlock that protects all the driver data structures
  * @priv:		Stores a pointer to the struct usb_hcd
@@ -958,6 +959,7 @@ struct dwc2_hsotg {
 	struct usb_phy *uphy;
 	struct dwc2_hsotg_plat *plat;
 	struct regulator_bulk_data supplies[DWC2_NUM_SUPPLIES];
+	struct regulator *vbus_supply;
 	u32 phyif;
 
 	spinlock_t lock;

drivers/usb/dwc2/hcd.c

@@ -356,6 +356,23 @@ static void dwc2_gusbcfg_init(struct dwc2_hsotg *hsotg)
 	dwc2_writel(usbcfg, hsotg->regs + GUSBCFG);
 }
 
+static int dwc2_vbus_supply_init(struct dwc2_hsotg *hsotg)
+{
+	hsotg->vbus_supply = devm_regulator_get_optional(hsotg->dev, "vbus");
+	if (IS_ERR(hsotg->vbus_supply))
+		return 0;
+
+	return regulator_enable(hsotg->vbus_supply);
+}
+
+static int dwc2_vbus_supply_exit(struct dwc2_hsotg *hsotg)
+{
+	if (hsotg->vbus_supply)
+		return regulator_disable(hsotg->vbus_supply);
+
+	return 0;
+}
+
 /**
  * dwc2_enable_host_interrupts() - Enables the Host mode interrupts
  *
@@ -3275,6 +3292,7 @@ static void dwc2_conn_id_status_change(struct work_struct *work)
 
 	/* B-Device connector (Device Mode) */
 	if (gotgctl & GOTGCTL_CONID_B) {
+		dwc2_vbus_supply_exit(hsotg);
 		/* Wait for switch to device mode */
 		dev_dbg(hsotg->dev, "connId B\n");
 		if (hsotg->bus_suspended) {
@@ -4323,6 +4341,9 @@ static int _dwc2_hcd_start(struct usb_hcd *hcd)
 	}
 
 	spin_unlock_irqrestore(&hsotg->lock, flags);
+
+	dwc2_vbus_supply_init(hsotg);
+
 	return 0;
 }
 
@@ -4350,6 +4371,8 @@ static void _dwc2_hcd_stop(struct usb_hcd *hcd)
 	clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
 	spin_unlock_irqrestore(&hsotg->lock, flags);
 
+	dwc2_vbus_supply_exit(hsotg);
+
 	usleep_range(1000, 3000);
 }
 
@@ -4386,6 +4409,7 @@ static int _dwc2_hcd_suspend(struct usb_hcd *hcd)
 		hprt0 |= HPRT0_SUSP;
 		hprt0 &= ~HPRT0_PWR;
 		dwc2_writel(hprt0, hsotg->regs + HPRT0);
+		dwc2_vbus_supply_exit(hsotg);
 	}
 
 	/* Enter partial_power_down */
@@ -4466,6 +4490,8 @@ static int _dwc2_hcd_resume(struct usb_hcd *hcd)
 		spin_unlock_irqrestore(&hsotg->lock, flags);
 		dwc2_port_resume(hsotg);
 	} else {
+		dwc2_vbus_supply_init(hsotg);
+
 		/* Wait for controller to correctly update D+/D- level */
 		usleep_range(3000, 5000);