[RFC] usb: xhci-dwc3: Support role switch default role

[Mark Kettenis]

When the device tree indicates support for role switching through
the "usb-role-switch" property, take the "role-switch-default-mode"
property into account when deciding which role to put the
controller into.

This makes USB devices work on Apple M1 systems where the device
tree may include a "dr_mode" property that is set to "otg", but
where we need to put the controller into "host" mode to see
devices connected to the type-C ports.

Signed-off-by: Mark Kettenis <kettenis at openbsd.org>
---

I'm far from sure this is the right approach.  But it does appear that
U-Boot doesn't really support role switching.  So making sure U-Boot
uses the default role defined in the device tree makes sense to me.

 drivers/usb/common/common.c  | 16 ++++++++++++++++
 drivers/usb/host/xhci-dwc3.c |  6 ++++++
 include/linux/usb/otg.h      | 10 ++++++++++
 3 files changed, 32 insertions(+)

diff --git a/drivers/usb/common/common.c b/drivers/usb/common/common.c
index ee0c064f1f..cff86a51ae 100644
--- a/drivers/usb/common/common.c
+++ b/drivers/usb/common/common.c
@@ -40,6 +40,22 @@ enum usb_dr_mode usb_get_dr_mode(ofnode node)
 	return USB_DR_MODE_UNKNOWN;
 }
 
+enum usb_dr_mode usb_get_role_switch_default_mode(ofnode node)
+{
+	const char *dr_mode;
+	int i;
+
+	dr_mode = ofnode_read_string(node, "role-switch-default-mode");
+	if (!dr_mode)
+		return USB_DR_MODE_UNKNOWN;
+
+	for (i = 0; i < ARRAY_SIZE(usb_dr_modes); i++)
+		if (!strcmp(dr_mode, usb_dr_modes[i]))
+			return i;
+
+	return USB_DR_MODE_UNKNOWN;
+}
+
 static const char *const speed_names[] = {
 	[USB_SPEED_UNKNOWN] = "UNKNOWN",
 	[USB_SPEED_LOW] = "low-speed",
diff --git a/drivers/usb/host/xhci-dwc3.c b/drivers/usb/host/xhci-dwc3.c
index bec0d98081..1dbd65dfaa 100644
--- a/drivers/usb/host/xhci-dwc3.c
+++ b/drivers/usb/host/xhci-dwc3.c
@@ -209,6 +209,12 @@ static int xhci_dwc3_probe(struct udevice *dev)
 	writel(reg, &dwc3_reg->g_usb2phycfg[0]);
 
 	dr_mode = usb_get_dr_mode(dev_ofnode(dev));
+	if (dr_mode == USB_DR_MODE_OTG &&
+	    dev_read_bool(dev, "usb-role-switch")) {
+		dr_mode = usb_get_role_switch_default_mode(dev_ofnode(dev));
+		if (dr_mode == USB_DR_MODE_UNKNOWN)
+			dr_mode = USB_DR_MODE_OTG;
+	}
 	if (dr_mode == USB_DR_MODE_UNKNOWN)
 		/* by default set dual role mode to HOST */
 		dr_mode = USB_DR_MODE_HOST;
diff --git a/include/linux/usb/otg.h b/include/linux/usb/otg.h
index c19b916be9..5d0dac950e 100644
--- a/include/linux/usb/otg.h
+++ b/include/linux/usb/otg.h
@@ -27,6 +27,16 @@ enum usb_dr_mode {
  */
 enum usb_dr_mode usb_get_dr_mode(ofnode node);
 
+/**
+ * usb_get_dr_mode() - Get dual role mode for given device
+ * @node: ofnode of the given device
+ *
+ * The function gets phy interface string from property
+ * 'role-switch-defaulr-mode', and returns the correspondig enum
+ * usb_dr_mode
+ */
+enum usb_dr_mode usb_get_role_switch_default_mode(ofnode node);
+
 /**
  * usb_get_maximum_speed() - Get maximum speed for given device
  * @node: ofnode of the given device
-- 
2.34.1