This is a note to let you know that I've just added the patch titled
tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done
to the 4.4-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-atmel-rs485-half-duplex-w-dma-enable-rx-after-tx-is-done.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b389f173aaa1204d6dc1f299082a162eb0491545 Mon Sep 17 00:00:00 2001
From: Richard Genoud <richard.genoud@xxxxxxxxx>
Date: Tue, 6 Dec 2016 13:05:33 +0100
Subject: tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done
From: Richard Genoud <richard.genoud@xxxxxxxxx>
commit b389f173aaa1204d6dc1f299082a162eb0491545 upstream.
When using RS485 in half duplex, RX should be enabled when TX is
finished, and stopped when TX starts.
Before commit 0058f0871efe7b01c6 ("tty/serial: atmel: fix RS485 half
duplex with DMA"), RX was not disabled in atmel_start_tx() if the DMA
was used. So, collisions could happened.
But disabling RX in atmel_start_tx() uncovered another bug:
RX was enabled again in the wrong place (in atmel_tx_dma) instead of
being enabled when TX is finished (in atmel_complete_tx_dma), so the
transmission simply stopped.
This bug was not triggered before commit 0058f0871efe7b01c6
("tty/serial: atmel: fix RS485 half duplex with DMA") because RX was
never disabled before.
Moving atmel_start_rx() in atmel_complete_tx_dma() corrects the problem.
Reported-by: Gil Weber <webergil@xxxxxxxxx>
Fixes: 0058f0871efe7b01c6
Tested-by: Gil Weber <webergil@xxxxxxxxx>
Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx>
Acked-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>
Tested-by: Bryan Evenson <bevenson@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/atmel_serial.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -810,6 +810,11 @@ static void atmel_complete_tx_dma(void *
*/
if (!uart_circ_empty(xmit))
tasklet_schedule(&atmel_port->tasklet);
+ else if ((port->rs485.flags & SER_RS485_ENABLED) &&
+ !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
+ /* DMA done, stop TX, start RX for RS485 */
+ atmel_start_rx(port);
+ }
spin_unlock_irqrestore(&port->lock, flags);
}
@@ -912,12 +917,6 @@ static void atmel_tx_dma(struct uart_por
desc->callback = atmel_complete_tx_dma;
desc->callback_param = atmel_port;
atmel_port->cookie_tx = dmaengine_submit(desc);
-
- } else {
- if (port->rs485.flags & SER_RS485_ENABLED) {
- /* DMA done, stop TX, start RX for RS485 */
- atmel_start_rx(port);
- }
}
if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
Patches currently in stable-queue which might be from richard.genoud@xxxxxxxxx are
queue-4.4/tty-serial-atmel-rs485-half-duplex-w-dma-enable-rx-after-tx-is-done.patch