[PATCH] serial: pxa: brief description

[PATCH] serial: pxa: brief description

[Marcus Folkesson]

I had a problem with a pxa270-based custom board when using the UART on
high speed (921.6 kbit/s).
The symptom was that the whole system just hangs sporadically.

After this work around was implemented the system seems to behave good.

In fact, I don't really see why the system should hang since there is a 
max counter, so the loop cannot run forever.

The patch is tested on kernel version 2.6.32, but the driver is allmost
the same.

Please take a look.
Feedback is very much appreciated

[PATCH] serial: pxa: work around for errata #20

[Marcus Folkesson]

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>
---
 drivers/tty/serial/pxa.c |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/serial/pxa.c b/drivers/tty/serial/pxa.c
index 531931c..5c8e3bb 100644
--- 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)
-- 
1.7.4.1

high speed (921.6 kbit/s).

[marcus.folkesson]

After this work around was implemented the system seems to behave good.

In fact, I don't really see why the system should hang since there is a 
max counter, so the loop cannot run forever.

The patch is tested on kernel version 2.6.32, but the driver is allmost
the same.

Please take a look.
Feedback is very much appreciated

>From Marcus Folkesson <marcus.folkesson@combitech.se> # This line is ignored.
From: Marcus Folkesson <marcus.folkesson@combitech.se>
Subject: [PATCH] serial: pxa: a brief description
In-Reply-To: marcus.folkesson@gmail.com

[PATCH] serial: pxa: work around for errata #20

[marcus.folkesson]

From: Marcus Folkesson <marcus.folkesson@gmail.com>

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>
---
 drivers/tty/serial/pxa.c |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/serial/pxa.c b/drivers/tty/serial/pxa.c
index 531931c..5c8e3bb 100644
--- 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)
-- 
1.7.4.1