usb: musb: Perform only write access on MUSB_INTRRXE

This is part of the workaround for AM35x advisory Advisory 1.1.20.
The advisory says that the IPSS bridge can't handle 8 & 16 bit read
access. An 16bit read access to MUSB_INTRRXE results in an 32bit read
access which also reads INTRUSB and therefore may lose interrupts.
This patch uses a shadow register of MUSB_INTRRXE so we only perform
write access to it.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_core.c

@@ -725,7 +725,8 @@ static irqreturn_t musb_stage0_irq(struct musb *musb, u8 int_usb,
 			/* REVISIT HNP; just force disconnect */
 		}
 		musb_writew(musb->mregs, MUSB_INTRTXE, musb->epmask);
-		musb_writew(musb->mregs, MUSB_INTRRXE, musb->epmask & 0xfffe);
+		musb->intrrxe = musb->epmask & 0xfffe;
+		musb_writew(musb->mregs, MUSB_INTRRXE, musb->intrrxe);
 		musb_writeb(musb->mregs, MUSB_INTRUSBE, 0xf7);
 		musb->port1_status &= ~(USB_PORT_STAT_LOW_SPEED
 					|USB_PORT_STAT_HIGH_SPEED
@@ -947,7 +948,8 @@ void musb_start(struct musb *musb)
 
 	/*  Set INT enable registers, enable interrupts */
 	musb_writew(regs, MUSB_INTRTXE, musb->epmask);
-	musb_writew(regs, MUSB_INTRRXE, musb->epmask & 0xfffe);
+	musb->intrrxe = musb->epmask & 0xfffe;
+	musb_writew(regs, MUSB_INTRRXE, musb->intrrxe);
 	musb_writeb(regs, MUSB_INTRUSBE, 0xf7);
 
 	musb_writeb(regs, MUSB_TESTMODE, 0);
@@ -986,6 +988,7 @@ static void musb_generic_disable(struct musb *musb)
 	/* disable interrupts */
 	musb_writeb(mbase, MUSB_INTRUSBE, 0);
 	musb_writew(mbase, MUSB_INTRTXE, 0);
+	musb->intrrxe = 0;
 	musb_writew(mbase, MUSB_INTRRXE, 0);
 
 	/* off */
@@ -2122,7 +2125,6 @@ static void musb_save_context(struct musb *musb)
 	musb->context.busctl = musb_read_ulpi_buscontrol(musb->mregs);
 	musb->context.power = musb_readb(musb_base, MUSB_POWER);
 	musb->context.intrtxe = musb_readw(musb_base, MUSB_INTRTXE);
-	musb->context.intrrxe = musb_readw(musb_base, MUSB_INTRRXE);
 	musb->context.intrusbe = musb_readb(musb_base, MUSB_INTRUSBE);
 	musb->context.index = musb_readb(musb_base, MUSB_INDEX);
 	musb->context.devctl = musb_readb(musb_base, MUSB_DEVCTL);
@@ -2196,7 +2198,7 @@ static void musb_restore_context(struct musb *musb)
 	musb_write_ulpi_buscontrol(musb->mregs, musb->context.busctl);
 	musb_writeb(musb_base, MUSB_POWER, musb->context.power);
 	musb_writew(musb_base, MUSB_INTRTXE, musb->context.intrtxe);
-	musb_writew(musb_base, MUSB_INTRRXE, musb->context.intrrxe);
+	musb_writew(musb_base, MUSB_INTRRXE, musb->intrrxe);
 	musb_writeb(musb_base, MUSB_INTRUSBE, musb->context.intrusbe);
 	musb_writeb(musb_base, MUSB_DEVCTL, musb->context.devctl);
 

drivers/usb/musb/musb_core.h

@@ -288,7 +288,7 @@ struct musb_csr_regs {
 struct musb_context_registers {
 
 	u8 power;
-	u16 intrtxe, intrrxe;
+	u16 intrtxe;
 	u8 intrusbe;
 	u16 frame;
 	u8 index, testmode;
@@ -313,6 +313,7 @@ struct musb {
 	struct work_struct	irq_work;
 	u16			hwvers;
 
+	u16			intrrxe;
 /* this hub status bit is reserved by USB 2.0 and not seen by usbcore */
 #define MUSB_PORT_STAT_RESUME	(1 << 31)
 

drivers/usb/musb/musb_gadget.c

@@ -1108,7 +1108,6 @@ static int musb_gadget_enable(struct usb_ep *ep,
 		musb_writew(regs, MUSB_TXCSR, csr);
 
 	} else {
-		u16 int_rxe = musb_readw(mbase, MUSB_INTRRXE);
 
 		if (hw_ep->is_shared_fifo)
 			musb_ep->is_in = 0;
@@ -1120,8 +1119,8 @@ static int musb_gadget_enable(struct usb_ep *ep,
 			goto fail;
 		}
 
-		int_rxe |= (1 << epnum);
-		musb_writew(mbase, MUSB_INTRRXE, int_rxe);
+		musb->intrrxe |= (1 << epnum);
+		musb_writew(mbase, MUSB_INTRRXE, musb->intrrxe);
 
 		/* REVISIT if can_bulk_combine() use by updating "tmp"
 		 * likewise high bandwidth periodic rx
@@ -1214,9 +1213,8 @@ static int musb_gadget_disable(struct usb_ep *ep)
 		musb_writew(musb->mregs, MUSB_INTRTXE, int_txe);
 		musb_writew(epio, MUSB_TXMAXP, 0);
 	} else {
-		u16 int_rxe = musb_readw(musb->mregs, MUSB_INTRRXE);
-		int_rxe &= ~(1 << epnum);
-		musb_writew(musb->mregs, MUSB_INTRRXE, int_rxe);
+		musb->intrrxe &= ~(1 << epnum);
+		musb_writew(musb->mregs, MUSB_INTRRXE, musb->intrrxe);
 		musb_writew(epio, MUSB_RXMAXP, 0);
 	}