serial: pxa: work around for errata #20

Errata E20: UART: Character Timeout interrupt remains set under certain
software conditions.

Implication: The software servicing the UART can be trapped in an infinite loop.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/tty/serial/pxa.c b/drivers/tty/serial/pxa.c
index 531931c..5c8e3bb 100644 (file)
--- a/drivers/tty/serial/pxa.c
+++ b/drivers/tty/serial/pxa.c
@@ -100,6 +100,16 @@ static inline void receive_chars(struct uart_pxa_port *up, int *status)
        int max_count = 256;
 
        do {
+               /* work around Errata #20 according to
+                * Intel(R) PXA27x Processor Family
+                * Specification Update (May 2005)
+                *
+                * Step 2
+                * Disable the Reciever Time Out Interrupt via IER[RTOEI]
+                */
+               up->ier &= ~UART_IER_RTOIE;
+               serial_out(up, UART_IER, up->ier);
+
                ch = serial_in(up, UART_RX);
                flag = TTY_NORMAL;
                up->port.icount.rx++;
@@ -156,6 +166,16 @@ static inline void receive_chars(struct uart_pxa_port *up, int *status)
                *status = serial_in(up, UART_LSR);
        } while ((*status & UART_LSR_DR) && (max_count-- > 0));
        tty_flip_buffer_push(tty);
+
+       /* work around Errata #20 according to
+        * Intel(R) PXA27x Processor Family
+        * Specification Update (May 2005)
+        *
+        * Step 6:
+        * No more data in FIFO: Re-enable RTO interrupt via IER[RTOIE]
+        */
+       up->ier |= UART_IER_RTOIE;
+       serial_out(up, UART_IER, up->ier);
 }
 
 static void transmit_chars(struct uart_pxa_port *up)