[PATCH v3] serial: PL011: clear pending interrupts

[Linus Walleij]

From: Linus Walleij <linus.walleij at linaro.org>

Chanho Min reported that when the boot loader transfers
control to the kernel, there may be pending interrupts
causing the UART to lock up in an eternal loop trying to
pick tokens from the FIFO (since the RX interrupt flag
indicates there are tokens) while in practice there are
no tokens - in fact there is only a pending IRQ flag.

This patch address the issue with a combination of two
patches suggested by Russell King that clears and mask
all interrupts at probe() and clears any pending error
and RX interrupts at port startup time.

We suspect the spurious interrupts are a side-effect of
switching the UART from FIFO to non-FIFO mode.

Cc: stable at kernel.org
Cc: Shreshtha Kumar Sahu <shreshthakumar.sahu at stericsson.com>
Cc: Jong-Sung Kim <neidhard.kim at lge.com>
Reported-by: Chanho Min <chanho0207 at gmail.com>
Suggested-by: Russell King <linux at arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
ChangeLog v1->v2:
- Instead of making the IRQ fastpath account for spurious
  IRQs with zero characters, make sure to clear out any
  pending IRQ flags in startup().
ChangeLog v2->v3:
- Attempt to clear out any spuriously appearing RX interrups
  in startup() instead of in the interrupt handler. Let's
  see if this works.
---
 drivers/tty/serial/amba-pl011.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 6800f5f..7e01399 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1381,6 +1381,10 @@ static int pl011_startup(struct uart_port *port)
 
 	uap->port.uartclk = clk_get_rate(uap->clk);
 
+	/* Clear pending error and receive interrupts */
+	writew(UART011_OEIS | UART011_BEIS | UART011_PEIS | UART011_FEIS |
+	       UART011_RTIS | UART011_RXIS, uap->port.membase + UART011_ICR);
+
 	/*
 	 * Allocate the IRQ
 	 */
@@ -1417,10 +1421,6 @@ static int pl011_startup(struct uart_port *port)
 	cr |= UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
 	writew(cr, uap->port.membase + UART011_CR);
 
-	/* Clear pending error interrupts */
-	writew(UART011_OEIS | UART011_BEIS | UART011_PEIS | UART011_FEIS,
-	       uap->port.membase + UART011_ICR);
-
 	/*
 	 * initialise the old status of the modem signals
 	 */
@@ -1435,6 +1435,9 @@ static int pl011_startup(struct uart_port *port)
 	 * as well.
 	 */
 	spin_lock_irq(&uap->port.lock);
+	/* Clear out any spuriously appearing RX interrupts */
+	 writew(UART011_RTIS | UART011_RXIS,
+		uap->port.membase + UART011_ICR);
 	uap->im = UART011_RTIM;
 	if (!pl011_dma_rx_running(uap))
 		uap->im |= UART011_RXIM;
@@ -1927,6 +1930,10 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 		goto unmap;
 	}
 
+	/* Ensure interrupts from this UART are masked and cleared */
+	writew(0, uap->port.membase + UART011_IMSC);
+	writew(0xffff, uap->port.membase + UART011_ICR);
+
 	uap->vendor = vendor;
 	uap->lcrh_rx = vendor->lcrh_rx;
 	uap->lcrh_tx = vendor->lcrh_tx;
-- 
1.7.8