usb: gadget: atmel: support USB suspend

This patch adds support for USB suspend to the Atmel UDC.

When suspended, the UDC clock can be stopped, resulting in some power
savings.  The "wake up" interrupt will fire irregardless of whether the
clock is running or not, allowing the UDC clock to be restarted when the
USB master wants to wake the device again.

The IRQ state of this device is somewhat fiddly.  The "wake up" IRQ
seems to actually be a "bus activity" indicator; the IRQ is almost
continuously asserted so enabling this IRQ should only be done after a
suspend when the wake IRQ becomes relevant.  Similarly, the "suspend"
IRQ detects "bus inactivity" and may therefore fire together with a
"wake" if the two types of activity coincide during the period between
two IRQ handler invocations; therefore, it's important to ignore the
"suspend" IRQ while waiting for a wake-up.

This has been tested on a SAMA5D2 board.
Signed-off-by: Jonas Bonn <jonas@norrbonn.se>
CC: Cristian Birsan <cristian.birsan@microchip.com>
CC: Felipe Balbi <balbi@kernel.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Nicolas Ferre <nicolas.ferre@microchip.com>
CC: Alexandre Belloni <alexandre.belloni@bootlin.com>
CC: Ludovic Desroches <ludovic.desroches@microchip.com>
CC: linux-arm-kernel@lists.infradead.org
CC: linux-usb@vger.kernel.org
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/atmel_usba_udc.c

@@ -1703,6 +1703,9 @@ static void usba_dma_irq(struct usba_udc *udc, struct usba_ep *ep)
 	}
 }
 
+static int start_clock(struct usba_udc *udc);
+static void stop_clock(struct usba_udc *udc);
+
 static irqreturn_t usba_udc_irq(int irq, void *devid)
 {
 	struct usba_udc *udc = devid;
@@ -1717,10 +1720,13 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 	DBG(DBG_INT, "irq, status=%#08x\n", status);
 
 	if (status & USBA_DET_SUSPEND) {
-		toggle_bias(udc, 0);
-		usba_writel(udc, INT_CLR, USBA_DET_SUSPEND);
+		usba_writel(udc, INT_CLR, USBA_DET_SUSPEND|USBA_WAKE_UP);
 		usba_int_enb_set(udc, USBA_WAKE_UP);
+		usba_int_enb_clear(udc, USBA_DET_SUSPEND);
+		udc->suspended = true;
+		toggle_bias(udc, 0);
 		udc->bias_pulse_needed = true;
+		stop_clock(udc);
 		DBG(DBG_BUS, "Suspend detected\n");
 		if (udc->gadget.speed != USB_SPEED_UNKNOWN
 				&& udc->driver && udc->driver->suspend) {
@@ -1731,14 +1737,17 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 	}
 
 	if (status & USBA_WAKE_UP) {
+		start_clock(udc);
 		toggle_bias(udc, 1);
 		usba_writel(udc, INT_CLR, USBA_WAKE_UP);
-		usba_int_enb_clear(udc, USBA_WAKE_UP);
 		DBG(DBG_BUS, "Wake Up CPU detected\n");
 	}
 
 	if (status & USBA_END_OF_RESUME) {
+		udc->suspended = false;
 		usba_writel(udc, INT_CLR, USBA_END_OF_RESUME);
+		usba_int_enb_clear(udc, USBA_WAKE_UP);
+		usba_int_enb_set(udc, USBA_DET_SUSPEND);
 		generate_bias_pulse(udc);
 		DBG(DBG_BUS, "Resume detected\n");
 		if (udc->gadget.speed != USB_SPEED_UNKNOWN
@@ -1753,6 +1762,8 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 	if (dma_status) {
 		int i;
 
+		usba_int_enb_set(udc, USBA_DET_SUSPEND);
+
 		for (i = 1; i <= USBA_NR_DMAS; i++)
 			if (dma_status & (1 << i))
 				usba_dma_irq(udc, &udc->usba_ep[i]);
@@ -1762,6 +1773,8 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 	if (ep_status) {
 		int i;
 
+		usba_int_enb_set(udc, USBA_DET_SUSPEND);
+
 		for (i = 0; i < udc->num_ep; i++)
 			if (ep_status & (1 << i)) {
 				if (ep_is_control(&udc->usba_ep[i]))
@@ -1775,7 +1788,9 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 		struct usba_ep *ep0, *ep;
 		int i, n;
 
-		usba_writel(udc, INT_CLR, USBA_END_OF_RESET);
+		usba_writel(udc, INT_CLR,
+			USBA_END_OF_RESET|USBA_END_OF_RESUME
+			|USBA_DET_SUSPEND|USBA_WAKE_UP);
 		generate_bias_pulse(udc);
 		reset_all_endpoints(udc);
 
@@ -1802,6 +1817,11 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
 				| USBA_BF(BK_NUMBER, USBA_BK_NUMBER_ONE)));
 		usba_ep_writel(ep0, CTL_ENB,
 				USBA_EPT_ENABLE | USBA_RX_SETUP);
+
+		/* If we get reset while suspended... */
+		udc->suspended = false;
+		usba_int_enb_clear(udc, USBA_WAKE_UP);
+
 		usba_int_enb_set(udc, USBA_BF(EPT_INT, 1) |
 				      USBA_DET_SUSPEND | USBA_END_OF_RESUME);
 
@@ -1869,9 +1889,19 @@ static int usba_start(struct usba_udc *udc)
 	if (ret)
 		return ret;
 
+	if (udc->suspended)
+		return 0;
+
 	spin_lock_irqsave(&udc->lock, flags);
 	toggle_bias(udc, 1);
 	usba_writel(udc, CTRL, USBA_ENABLE_MASK);
+	/* Clear all requested and pending interrupts... */
+	usba_writel(udc, INT_ENB, 0);
+	udc->int_enb_cache = 0;
+	usba_writel(udc, INT_CLR,
+		USBA_END_OF_RESET|USBA_END_OF_RESUME
+		|USBA_DET_SUSPEND|USBA_WAKE_UP);
+	/* ...and enable just 'reset' IRQ to get us started */
 	usba_int_enb_set(udc, USBA_END_OF_RESET);
 	spin_unlock_irqrestore(&udc->lock, flags);
 
@@ -1882,6 +1912,9 @@ static void usba_stop(struct usba_udc *udc)
 {
 	unsigned long flags;
 
+	if (udc->suspended)
+		return;
+
 	spin_lock_irqsave(&udc->lock, flags);
 	udc->gadget.speed = USB_SPEED_UNKNOWN;
 	reset_all_endpoints(udc);
@@ -1909,6 +1942,7 @@ static irqreturn_t usba_vbus_irq_thread(int irq, void *devid)
 		if (vbus) {
 			usba_start(udc);
 		} else {
+			udc->suspended = false;
 			usba_stop(udc);
 
 			if (udc->driver->disconnect)
@@ -1972,6 +2006,7 @@ static int atmel_usba_stop(struct usb_gadget *gadget)
 	if (fifo_mode == 0)
 		udc->configured_ep = 1;
 
+	udc->suspended = false;
 	usba_stop(udc);
 
 	udc->driver = NULL;
@@ -2285,6 +2320,7 @@ static int usba_udc_suspend(struct device *dev)
 	mutex_lock(&udc->vbus_mutex);
 
 	if (!device_may_wakeup(dev)) {
+		udc->suspended = false;
 		usba_stop(udc);
 		goto out;
 	}
@@ -2294,10 +2330,13 @@ static int usba_udc_suspend(struct device *dev)
 	 * to request vbus irq, assuming always on.
 	 */
 	if (udc->vbus_pin) {
+		/* FIXME: right to stop here...??? */
 		usba_stop(udc);
 		enable_irq_wake(gpiod_to_irq(udc->vbus_pin));
 	}
 
+	enable_irq_wake(udc->irq);
+
 out:
 	mutex_unlock(&udc->vbus_mutex);
 	return 0;
@@ -2311,8 +2350,12 @@ static int usba_udc_resume(struct device *dev)
 	if (!udc->driver)
 		return 0;
 
-	if (device_may_wakeup(dev) && udc->vbus_pin)
-		disable_irq_wake(gpiod_to_irq(udc->vbus_pin));
+	if (device_may_wakeup(dev)) {
+		if (udc->vbus_pin)
+			disable_irq_wake(gpiod_to_irq(udc->vbus_pin));
+
+		disable_irq_wake(udc->irq);
+	}
 
 	/* If Vbus is present, enable the controller and wait for reset */
 	mutex_lock(&udc->vbus_mutex);

drivers/usb/gadget/udc/atmel_usba_udc.h

@@ -331,6 +331,7 @@ struct usba_udc {
 	struct usba_ep *usba_ep;
 	bool bias_pulse_needed;
 	bool clocked;
+	bool suspended;
 
 	u16 devstatus;