linux-kernel - [PATCH] usb: gadget: u_serial: Implement remote wakeup capability

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Message-Id: <20250424121142.4180241-1-prashanth.k@oss.qualcomm.com>
Date: Thu, 24 Apr 2025 17:41:42 +0530
From: Prashanth K <prashanth.k@....qualcomm.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeff Johnson <jeff.johnson@....qualcomm.com>,
        Michael Walle <mwalle@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Prashanth K <prashanth.k@....qualcomm.com>
Subject: [PATCH] usb: gadget: u_serial: Implement remote wakeup capability

Implement the remote wakeup capability for u_serial. The newly added
function gserial_wakeup_host() wakes up the host when there is some
data to be sent while the device is suspended. Add gser_get_status()
callbacks to advertise f_serial interface as function wakeup capable.

Signed-off-by: Prashanth K <prashanth.k@....qualcomm.com>
---
 drivers/usb/gadget/function/f_serial.c |  7 +++++
 drivers/usb/gadget/function/u_serial.c | 43 ++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/drivers/usb/gadget/function/f_serial.c b/drivers/usb/gadget/function/f_serial.c
index 8f7e7a2b2ff2..0f266bc067f5 100644
--- a/drivers/usb/gadget/function/f_serial.c
+++ b/drivers/usb/gadget/function/f_serial.c
@@ -364,6 +364,12 @@ static void gser_suspend(struct usb_function *f)
 	gserial_suspend(&gser->port);
 }
 
+static int gser_get_status(struct usb_function *f)
+{
+	return (f->func_wakeup_armed ? USB_INTRF_STAT_FUNC_RW : 0) |
+		USB_INTRF_STAT_FUNC_RW_CAP;
+}
+
 static struct usb_function *gser_alloc(struct usb_function_instance *fi)
 {
 	struct f_gser	*gser;
@@ -387,6 +393,7 @@ static struct usb_function *gser_alloc(struct usb_function_instance *fi)
 	gser->port.func.free_func = gser_free;
 	gser->port.func.resume = gser_resume;
 	gser->port.func.suspend = gser_suspend;
+	gser->port.func.get_status = gser_get_status;
 
 	return &gser->port.func;
 }
diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 36fff45e8c9b..41dee7c8cc7c 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -592,6 +592,17 @@ static int gs_start_io(struct gs_port *port)
 	return status;
 }
 
+static int gserial_wakeup_host(struct gserial *gser)
+{
+	struct usb_function	*func = &gser->func;
+	struct usb_gadget	*gadget = func->config->cdev->gadget;
+
+	if (func->func_suspended)
+		return usb_func_wakeup(func);
+	else
+		return usb_gadget_wakeup(gadget);
+}
+
 /*-------------------------------------------------------------------------*/
 
 /* TTY Driver */
@@ -746,6 +757,8 @@ static ssize_t gs_write(struct tty_struct *tty, const u8 *buf, size_t count)
 {
 	struct gs_port	*port = tty->driver_data;
 	unsigned long	flags;
+	int ret = 0;
+	struct gserial  *gser = port->port_usb;
 
 	pr_vdebug("gs_write: ttyGS%d (%p) writing %zu bytes\n",
 			port->port_num, tty, count);
@@ -753,6 +766,17 @@ static ssize_t gs_write(struct tty_struct *tty, const u8 *buf, size_t count)
 	spin_lock_irqsave(&port->port_lock, flags);
 	if (count)
 		count = kfifo_in(&port->port_write_buf, buf, count);
+
+	if (port->suspended) {
+		spin_unlock_irqrestore(&port->port_lock, flags);
+		ret = gserial_wakeup_host(gser);
+		if (ret) {
+			pr_debug("ttyGS%d: Remote wakeup failed:%d\n", port->port_num, ret);
+			return count;
+		}
+		spin_lock_irqsave(&port->port_lock, flags);
+	}
+
 	/* treat count == 0 as flush_chars() */
 	if (port->port_usb)
 		gs_start_tx(port);
@@ -781,10 +805,22 @@ static void gs_flush_chars(struct tty_struct *tty)
 {
 	struct gs_port	*port = tty->driver_data;
 	unsigned long	flags;
+	int ret = 0;
+	struct gserial  *gser = port->port_usb;
 
 	pr_vdebug("gs_flush_chars: (%d,%p)\n", port->port_num, tty);
 
 	spin_lock_irqsave(&port->port_lock, flags);
+	if (port->suspended) {
+		spin_unlock_irqrestore(&port->port_lock, flags);
+		ret = gserial_wakeup_host(gser);
+		if (ret) {
+			pr_debug("ttyGS%d: Remote wakeup failed:%d\n", port->port_num, ret);
+			return;
+		}
+		spin_lock_irqsave(&port->port_lock, flags);
+	}
+
 	if (port->port_usb)
 		gs_start_tx(port);
 	spin_unlock_irqrestore(&port->port_lock, flags);
@@ -1464,6 +1500,13 @@ void gserial_suspend(struct gserial *gser)
 		return;
 	}
 
+	if (port->write_busy || port->write_started) {
+		/* Wakeup to host if there are ongoing transfers */
+		spin_unlock_irqrestore(&serial_port_lock, flags);
+		if (!gserial_wakeup_host(gser))
+			return;
+	}
+
 	spin_lock(&port->port_lock);
 	spin_unlock(&serial_port_lock);
 	port->suspended = true;
-- 
2.25.1