usb: musb: core: fix TX/RX endpoint order

commit e3c93e1a upstream.

As per Mentor Graphics' documentation, we should
always handle TX endpoints before RX endpoints.

This patch fixes that error while also updating
some hard-to-read comments which were scattered
around musb_interrupt().

This patch should be backported as far back as
possible since this error has been in the driver
since it's conception.
Signed-off-by: Felipe Balbi <balbi@ti.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/usb/musb/musb_core.c

@@ -1520,16 +1520,30 @@ irqreturn_t musb_interrupt(struct musb *musb)
 		(devctl & MUSB_DEVCTL_HM) ? "host" : "peripheral",
 		musb->int_usb, musb->int_tx, musb->int_rx);
 
-	/* the core can interrupt us for multiple reasons; docs have
-	 * a generic interrupt flowchart to follow
+	/**
+	 * According to Mentor Graphics' documentation, flowchart on page 98,
+	 * IRQ should be handled as follows:
+	 *
+	 * . Resume IRQ
+	 * . Session Request IRQ
+	 * . VBUS Error IRQ
+	 * . Suspend IRQ
+	 * . Connect IRQ
+	 * . Disconnect IRQ
+	 * . Reset/Babble IRQ
+	 * . SOF IRQ (we're not using this one)
+	 * . Endpoint 0 IRQ
+	 * . TX Endpoints
+	 * . RX Endpoints
+	 *
+	 * We will be following that flowchart in order to avoid any problems
+	 * that might arise with internal Finite State Machine.
 	 */
+
 	if (musb->int_usb)
 		retval |= musb_stage0_irq(musb, musb->int_usb,
 				devctl);
 
-	/* "stage 1" is handling endpoint irqs */
-
-	/* handle endpoint 0 first */
 	if (musb->int_tx & 1) {
 		if (devctl & MUSB_DEVCTL_HM)
 			retval |= musb_h_ep0_irq(musb);
@@ -1537,37 +1551,31 @@ irqreturn_t musb_interrupt(struct musb *musb)
 			retval |= musb_g_ep0_irq(musb);
 	}
 
-	/* RX on endpoints 1-15 */
-	reg = musb->int_rx >> 1;
+	reg = musb->int_tx >> 1;
 	ep_num = 1;
 	while (reg) {
 		if (reg & 1) {
-			/* musb_ep_select(musb->mregs, ep_num); */
-			/* REVISIT just retval = ep->rx_irq(...) */
 			retval = IRQ_HANDLED;
 			if (devctl & MUSB_DEVCTL_HM)
-				musb_host_rx(musb, ep_num);
+				musb_host_tx(musb, ep_num);
 			else
-				musb_g_rx(musb, ep_num);
+				musb_g_tx(musb, ep_num);
 		}
-
 		reg >>= 1;
 		ep_num++;
 	}
 
-	/* TX on endpoints 1-15 */
-	reg = musb->int_tx >> 1;
+	reg = musb->int_rx >> 1;
 	ep_num = 1;
 	while (reg) {
 		if (reg & 1) {
-			/* musb_ep_select(musb->mregs, ep_num); */
-			/* REVISIT just retval |= ep->tx_irq(...) */
 			retval = IRQ_HANDLED;
 			if (devctl & MUSB_DEVCTL_HM)
-				musb_host_tx(musb, ep_num);
+				musb_host_rx(musb, ep_num);
 			else
-				musb_g_tx(musb, ep_num);
+				musb_g_rx(musb, ep_num);
 		}
+
 		reg >>= 1;
 		ep_num++;
 	}