usb: dwc3: meson-g12a: support the GXL/GXM DWC3 host phy disconnect

On the Amlogic GXL/GXM SoCs, the OTG PHY status signals are always
connected to the DWC3 controller, thus crashing the controller when
switching to OTG mode when port is not populated with a device/cable to
Host.

Amlogic added a bit to disconnect the OTG PHY status signals from the DWC3
to be used when switching the OTG PHY as Device to the DWC2 controller.

The drawback is that it makes the DWC3 port state machine stall and needs
a full reset of the DWC3 controller to get connect status to the port
connected to the OTG PHY, but not the other one.
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/dwc3/dwc3-meson-g12a.c

@@ -131,6 +131,7 @@ struct dwc3_meson_g12a;
 
 struct dwc3_meson_g12a_drvdata {
 	bool otg_switch_supported;
+	bool otg_phy_host_port_disable;
 	struct clk_bulk_data *clks;
 	int num_clks;
 	const char **phy_names;
@@ -155,6 +156,19 @@ static int dwc3_meson_g12a_set_phy_mode(struct dwc3_meson_g12a *priv,
 
 static int dwc3_meson_g12a_usb_init(struct dwc3_meson_g12a *priv);
 
+/*
+ * For GXL and GXM SoCs:
+ * USB Phy muxing between the DWC2 Device controller and the DWC3 Host
+ * controller is buggy when switching from Device to Host when USB port
+ * is unpopulated, it causes the DWC3 to hard crash.
+ * When populated (including OTG switching with ID pin), the switch works
+ * like a charm like on the G12A platforms.
+ * In order to still switch from Host to Device on an USB Type-A port,
+ * an U2_PORT_DISABLE bit has been added to disconnect the DWC3 Host
+ * controller from the port, but when used the DWC3 controller must be
+ * reset to recover usage of the port.
+ */
+
 static struct dwc3_meson_g12a_drvdata g12a_drvdata = {
 	.otg_switch_supported = true,
 	.clks = meson_g12a_clocks,
@@ -290,6 +304,14 @@ static void dwc3_meson_g12a_usb_otg_apply_mode(struct dwc3_meson_g12a *priv,
 					       enum phy_mode mode)
 {
 	if (mode == PHY_MODE_USB_DEVICE) {
+		if (priv->otg_mode != USB_DR_MODE_OTG &&
+		    priv->drvdata->otg_phy_host_port_disable)
+			/* Isolate the OTG PHY port from the Host Controller */
+			regmap_update_bits(priv->usb_glue_regmap, USB_R1,
+				USB_R1_U3H_HOST_U2_PORT_DISABLE_MASK,
+				FIELD_PREP(USB_R1_U3H_HOST_U2_PORT_DISABLE_MASK,
+					   BIT(USB2_OTG_PHY)));
+
 		regmap_update_bits(priv->usb_glue_regmap, USB_R0,
 				USB_R0_U2D_ACT, USB_R0_U2D_ACT);
 		regmap_update_bits(priv->usb_glue_regmap, USB_R0,
@@ -297,6 +319,12 @@ static void dwc3_meson_g12a_usb_otg_apply_mode(struct dwc3_meson_g12a *priv,
 		regmap_update_bits(priv->usb_glue_regmap, USB_R4,
 				USB_R4_P21_SLEEP_M0, USB_R4_P21_SLEEP_M0);
 	} else {
+		if (priv->otg_mode != USB_DR_MODE_OTG &&
+		    priv->drvdata->otg_phy_host_port_disable) {
+			regmap_update_bits(priv->usb_glue_regmap, USB_R1,
+				USB_R1_U3H_HOST_U2_PORT_DISABLE_MASK, 0);
+			msleep(500);
+		}
 		regmap_update_bits(priv->usb_glue_regmap, USB_R0,
 				USB_R0_U2D_ACT, 0);
 		regmap_update_bits(priv->usb_glue_regmap, USB_R4,
@@ -430,6 +458,13 @@ static int dwc3_meson_g12a_role_set(struct usb_role_switch *sw,
 	if (mode == priv->otg_phy_mode)
 		return 0;
 
+	if (priv->drvdata->otg_phy_host_port_disable)
+		dev_warn_once(priv->dev, "Manual OTG switch is broken on this "\
+					 "SoC, when manual switching from "\
+					 "Host to device, DWC3 controller "\
+					 "will need to be resetted in order "\
+					 "to recover usage of the Host port");
+
 	return dwc3_meson_g12a_otg_mode_set(priv, mode);
 }