linux-kernel - [014/264] serial: pxa: work around for errata #20

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Date:	Wed, 09 Nov 2011 13:31:01 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Marcus Folkesson <marcus.folkesson@...il.com>
Subject: [014/264] serial: pxa: work around for errata #20

3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit e44aabd649c80e8be16ede3ed3cbff6fb2561ca9 upstream.

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@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/tty/serial/pxa.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/drivers/tty/serial/pxa.c
+++ b/drivers/tty/serial/pxa.c
@@ -100,6 +100,16 @@ static inline void receive_chars(struct
 	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
 		*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)


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