[PATCH v5 6/9] usb: misc: qcom_eud: add role-based EUD control

[Elson Serrao <elson.serrao@oss.qualcomm.com>]

EUD functions by presenting itself as a USB device to the host PC and is
therefore only applicable when the port operates in device role. Keeping
EUD enabled in other roles provides no benefit and unnecessarily keeps
the associated PHY resources enabled. Furthermore, enabling EUD in host
role can cause the USB controller to misbehave because the EUD hub
supports only a single upstream-facing port.

Address this by treating EUD as usable only in device role. The
role-switch callback enables or disables EUD as the port enters or
leaves device role. A sysfs enable request made outside device role is
recorded and honored when the port subsequently switches to device role.

Signed-off-by: Elson Serrao <elson.serrao@oss.qualcomm.com>
---
 drivers/usb/misc/qcom_eud.c | 46 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
index e83a4402e4b8..538e070cc140 100644
--- a/drivers/usb/misc/qcom_eud.c
+++ b/drivers/usb/misc/qcom_eud.c
@@ -15,6 +15,7 @@
 #include <linux/phy/phy.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
+#include <linux/string_choices.h>
 #include <linux/sysfs.h>
 #include <linux/usb/role.h>
 #include <linux/firmware/qcom/qcom_scm.h>
@@ -55,6 +56,8 @@ struct eud_chip {
 	struct device			*dev;
 	void __iomem			*base;
 	struct eud_path			*paths[EUD_MAX_PORTS];
+	/* serializes EUD control operations */
+	struct mutex			state_lock;
 	phys_addr_t			mode_mgr;
 	unsigned int			int_status;
 	int				irq;
@@ -156,17 +159,33 @@ static ssize_t enable_store(struct device *dev,
 		const char *buf, size_t count)
 {
 	struct eud_chip *chip = dev_get_drvdata(dev);
+	struct eud_path *path;
 	bool enable;
 	int ret;
 
 	if (kstrtobool(buf, &enable))
 		return -EINVAL;
 
+	guard(mutex)(&chip->state_lock);
+
 	/* Skip operation if already in desired state */
 	if (chip->enabled == enable)
 		return count;
 
 	if (enable) {
+		path = chip->paths[chip->port_idx];
+
+		/*
+		 * If not yet in device role, honor the userspace request and defer
+		 * EUD enablement until the port transitions to device role in the
+		 * set_role callback.
+		 */
+		if (path->curr_role != USB_ROLE_DEVICE) {
+			dev_info(chip->dev, "Deferring EUD enable until port enters device mode\n");
+			chip->enabled = enable;
+			return count;
+		}
+
 		ret = enable_eud(chip);
 		if (ret) {
 			dev_err(chip->dev, "failed to enable eud\n");
@@ -304,7 +323,30 @@ static irqreturn_t handle_eud_irq_thread(int irq, void *data)
 static int eud_role_switch_set(struct usb_role_switch *sw, enum usb_role role)
 {
 	struct eud_path *path = usb_role_switch_get_drvdata(sw);
-	int ret;
+	struct eud_chip *chip = path->chip;
+	int ret = 0;
+
+	guard(mutex)(&chip->state_lock);
+
+	/*
+	 * EUD is usable only in device role. Power it down for every other
+	 * role to avoid keeping an unusable module 'ON'. chip->enabled
+	 * preserves user's sysfs configuration and is not modified across
+	 * role transitions.
+	 */
+	if (chip->enabled && path->num == chip->port_idx && role != path->curr_role) {
+		if (role == USB_ROLE_DEVICE)
+			ret = enable_eud(chip);
+		else if (path->curr_role == USB_ROLE_DEVICE)
+			ret = disable_eud(chip);
+
+		if (ret) {
+			dev_err(chip->dev, "failed to %s EUD for role %s: %d\n",
+				str_enable_disable(role == USB_ROLE_DEVICE),
+				usb_role_string(role), ret);
+			return ret;
+		}
+	}
 
 	/* Forward the role request to the USB controller */
 	ret = usb_role_switch_set_role(path->controller_sw, role);
@@ -431,6 +473,8 @@ static int eud_probe(struct platform_device *pdev)
 
 	chip->dev = &pdev->dev;
 
+	mutex_init(&chip->state_lock);
+
 	for_each_child_of_node_scoped(np, child) {
 		ret = eud_init_path(chip, child);
 		if (ret)
-- 
2.34.1