[RFC] usb: musb: dsps, OTG detection

[Markus Pargmann]

The USB Controller does not support ID pin change interrupts. So we have
to use a polling function to detect changes of A/B device state
(otg_timer). This poll function has to check in several states if a
other device type might be connected to the USB port. This check is
triggered by manually starting/stopping a USB Session.

So in A mode, we cancel the currently running session which also
disables the possibility to detect new devices via interrupt. In B mode,
we start a session to check for ID-Pin and possibly connected devices.

Whenever a real USB session ends, we have to trigger the otg_timer poll
function again.

Signed-off-by: Markus Pargmann <mpa at pengutronix.de>
---
 drivers/usb/musb/musb_dsps.c | 84 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 78 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/musb/musb_dsps.c b/drivers/usb/musb/musb_dsps.c
index b24b697..0245e8d 100644
--- a/drivers/usb/musb/musb_dsps.c
+++ b/drivers/usb/musb/musb_dsps.c
@@ -178,6 +178,43 @@ static const struct file_operations musb_regdump_fops = {
 
 #endif /* IS_ENABLED(CONFIG_DEBUG_FS) */
 
+/*
+ * Compare driver and hardware mode and update driver state if necessary.
+ * Not all hardware changes actually reach the driver through interrupts.
+ */
+static void dsps_update_mode(struct musb *musb)
+{
+	u8 devctl;
+
+	devctl = dsps_readb(musb->mregs, MUSB_DEVCTL);
+
+	switch (musb->xceiv->state) {
+	case OTG_STATE_A_IDLE:
+		if (devctl & MUSB_DEVCTL_BDEVICE) {
+			dev_dbg(musb->controller, "detected controller state B, software state A\n");
+			musb->xceiv->state = OTG_STATE_B_IDLE;
+		}
+		break;
+	case OTG_STATE_B_IDLE:
+		if (!(devctl & MUSB_DEVCTL_BDEVICE)) {
+			dev_dbg(musb->controller, "detected controller state A, software state B\n");
+			musb->xceiv->state = OTG_STATE_A_IDLE;
+		}
+		break;
+	default:
+		if (!(devctl & MUSB_DEVCTL_SESSION)) {
+			dev_dbg(musb->controller, "detected controller out of session (%x), software state %s\n",
+				devctl,
+				usb_otg_state_string(musb->xceiv->state));
+			if (devctl & MUSB_DEVCTL_BDEVICE)
+				musb->xceiv->state = OTG_STATE_B_IDLE;
+			else
+				musb->xceiv->state = OTG_STATE_A_IDLE;
+		}
+		break;
+	}
+}
+
 /**
  * dsps_musb_enable - enable interrupts
  */
@@ -229,6 +266,8 @@ static void otg_timer(unsigned long _musb)
 	u8 devctl;
 	unsigned long flags;
 
+	dsps_update_mode(musb);
+
 	/*
 	 * We poll because DSPS IP's won't expose several OTG-critical
 	 * status change events (from the transceiver) otherwise.
@@ -239,6 +278,16 @@ static void otg_timer(unsigned long _musb)
 
 	spin_lock_irqsave(&musb->lock, flags);
 	switch (musb->xceiv->state) {
+	case OTG_STATE_A_IDLE:
+	case OTG_STATE_A_WAIT_VRISE:
+		/*
+		 * Poll the devctl register to know when the controller switches
+		 * back to B state.
+		 */
+		musb_writeb(mregs, MUSB_DEVCTL,
+				devctl & (~MUSB_DEVCTL_SESSION));
+		mod_timer(&glue->timer, jiffies + wrp->poll_seconds * HZ);
+		break;
 	case OTG_STATE_A_WAIT_BCON:
 		devctl &= ~MUSB_DEVCTL_SESSION;
 		dsps_writeb(musb->mregs, MUSB_DEVCTL, devctl);
@@ -251,6 +300,8 @@ static void otg_timer(unsigned long _musb)
 			musb->xceiv->state = OTG_STATE_A_IDLE;
 			MUSB_HST_MODE(musb);
 		}
+		mod_timer(&glue->timer,
+				jiffies + wrp->poll_seconds * HZ);
 		break;
 	case OTG_STATE_A_WAIT_VFALL:
 		musb->xceiv->state = OTG_STATE_A_WAIT_VRISE;
@@ -258,12 +309,24 @@ static void otg_timer(unsigned long _musb)
 			    MUSB_INTR_VBUSERROR << wrp->usb_shift);
 		break;
 	case OTG_STATE_B_IDLE:
+		/*
+		 * There's no ID-changed IRQ, so we have no good way to tell
+		 * when to switch to the A-Default state machine (by setting
+		 * the DEVCTL.Session bit).
+		 *
+		 * Workaround:  whenever we're in B_IDLE, try setting the
+		 * session flag every few seconds.  If it works, ID was
+		 * grounded and we're now in the A-Default state machine.
+		 *
+		 * NOTE: setting the session flag is _supposed_ to trigger
+		 * SRP but clearly it doesn't.
+		 */
+		musb_writeb(mregs, MUSB_DEVCTL, devctl | MUSB_DEVCTL_SESSION);
 		devctl = dsps_readb(mregs, MUSB_DEVCTL);
-		if (devctl & MUSB_DEVCTL_BDEVICE)
-			mod_timer(&glue->timer,
-					jiffies + wrp->poll_seconds * HZ);
-		else
+		if (!(devctl & MUSB_DEVCTL_BDEVICE))
 			musb->xceiv->state = OTG_STATE_A_IDLE;
+		mod_timer(&glue->timer,
+				jiffies + wrp->poll_seconds * HZ);
 		break;
 	default:
 		break;
@@ -376,7 +439,6 @@ static irqreturn_t dsps_interrupt(int irq, void *hci)
 			MUSB_HST_MODE(musb);
 			musb->xceiv->otg->default_a = 1;
 			musb->xceiv->state = OTG_STATE_A_WAIT_VRISE;
-			del_timer(&glue->timer);
 		} else {
 			musb->is_active = 0;
 			MUSB_DEV_MODE(musb);
@@ -397,8 +459,16 @@ static irqreturn_t dsps_interrupt(int irq, void *hci)
 		ret |= musb_interrupt(musb);
 
 	/* Poll for ID change */
-	if (musb->xceiv->state == OTG_STATE_B_IDLE)
+	switch (musb->xceiv->state) {
+	case OTG_STATE_A_IDLE:
+	case OTG_STATE_A_WAIT_BCON:
+	case OTG_STATE_A_WAIT_VRISE:
+	case OTG_STATE_B_IDLE:
 		mod_timer(&glue->timer, jiffies + wrp->poll_seconds * HZ);
+		break;
+	default:
+		break;
+	}
 out:
 	spin_unlock_irqrestore(&musb->lock, flags);
 
@@ -479,6 +549,8 @@ static int dsps_musb_init(struct musb *musb)
 
 	dev_info(dev, "%s:%d %s: OK\n", __FILE__, __LINE__, __func__);
 
+	musb->xceiv->otg->default_a = 0;
+
 	return 0;
 }
 
-- 
1.8.4.rc3