This is a note to let you know that I've just added the patch titled
tty: serial: fsl_lpuart: clear receive flag on FIFO flush
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tty-serial-fsl_lpuart-clear-receive-flag-on-fifo-flush.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 8e4934c6d6c659e22b1b746af4196683e77ce6ca Mon Sep 17 00:00:00 2001
From: Stefan Agner <[email protected]>
Date: Fri, 13 Mar 2015 14:51:51 +0100
Subject: tty: serial: fsl_lpuart: clear receive flag on FIFO flush
From: Stefan Agner <[email protected]>
commit 8e4934c6d6c659e22b1b746af4196683e77ce6ca upstream.
When the receiver was enabled during startup, a character could
have been in the FIFO when the UART get initially used. The
driver configures the (receive) watermark level, and flushes the
FIFO. However, the receive flag (RDRF) could still be set at that
stage (as mentioned in the register description of UARTx_RWFIFO).
This leads to an interrupt which won't be handled properly in
interrupt mode: The receive interrupt function lpuart_rxint checks
the FIFO count, which is 0 at that point (due to the flush
during initialization). The problem does not manifest when using
DMA to receive characters.
Fix this situation by explicitly read the status register, which
leads to clearing of the RDRF flag. Due to the flush just after
the status flag read, a explicit data read is not to required.
Signed-off-by: Stefan Agner <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/tty/serial/fsl_lpuart.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -910,6 +910,9 @@ static void lpuart_setup_watermark(struc
writeb(val | UARTPFIFO_TXFE | UARTPFIFO_RXFE,
sport->port.membase + UARTPFIFO);
+ /* explicitly clear RDRF */
+ readb(sport->port.membase + UARTSR1);
+
/* flush Tx and Rx FIFO */
writeb(UARTCFIFO_TXFLUSH | UARTCFIFO_RXFLUSH,
sport->port.membase + UARTCFIFO);
Patches currently in stable-queue which might be from [email protected] are
queue-3.19/iio-adc-vf610-use-adc-clock-within-specification.patch
queue-3.19/tty-serial-fsl_lpuart-clear-receive-flag-on-fifo-flush.patch
queue-3.19/tty-serial-fsl_lpuart-specify-transmit-fifo-size.patch
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