usb: dwc2: drd: fix dwc2_drd_role_sw_set when clock could be disabled

In case of USB_DR_MODE_PERIPHERAL, the OTG clock is disabled at the end of
the probe (it is not the case if USB_DR_MODE_HOST or USB_DR_MODE_OTG).
The clock is then enabled on udc_start.
If dwc2_drd_role_sw_set is called before udc_start (it is the case if the
usb cable is plugged at boot), GOTGCTL and GUSBCFG registers cannot be
read/written, so session cannot be overridden.
To avoid this case, check the ll_hw_enabled value and enable the clock if
it is available, and disable it after the override.

Fixes: 17f93402 ("usb: dwc2: override PHY input signals with usb role switch support")
Acked-by: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20211005095305.66397-3-amelie.delaunay@foss.st.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/drd.c

@@ -7,6 +7,7 @@
  * Author(s): Amelie Delaunay <amelie.delaunay@st.com>
  */
 
+#include <linux/clk.h>
 #include <linux/iopoll.h>
 #include <linux/platform_device.h>
 #include <linux/usb/role.h>
@@ -86,6 +87,20 @@ static int dwc2_drd_role_sw_set(struct usb_role_switch *sw, enum usb_role role)
 	}
 #endif
 
+	/*
+	 * In case of USB_DR_MODE_PERIPHERAL, clock is disabled at the end of
+	 * the probe and enabled on udc_start.
+	 * If role-switch set is called before the udc_start, we need to enable
+	 * the clock to read/write GOTGCTL and GUSBCFG registers to override
+	 * mode and sessions. It is the case if cable is plugged at boot.
+	 */
+	if (!hsotg->ll_hw_enabled && hsotg->clk) {
+		int ret = clk_prepare_enable(hsotg->clk);
+
+		if (ret)
+			return ret;
+	}
+
 	spin_lock_irqsave(&hsotg->lock, flags);
 
 	if (role == USB_ROLE_HOST) {
@@ -110,6 +125,9 @@ static int dwc2_drd_role_sw_set(struct usb_role_switch *sw, enum usb_role role)
 		/* This will raise a Connector ID Status Change Interrupt */
 		dwc2_force_mode(hsotg, role == USB_ROLE_HOST);
 
+	if (!hsotg->ll_hw_enabled && hsotg->clk)
+		clk_disable_unprepare(hsotg->clk);
+
 	dev_dbg(hsotg->dev, "%s-session valid\n",
 		role == USB_ROLE_NONE ? "No" :
 		role == USB_ROLE_HOST ? "A" : "B");