On an i.MX6Q based system using the imx-UART in rs485 mode the following
could be observed: When a character is supposed to be sent,
imx_start_tx() enables the Transmit Complete Interrupt (UCR4_TCEN) and
then enables DMA. If then the Transmit Complete Interrupt triggers
before the DMA request starts to send characters the irq handler
disables the Transmitter Empty Interrupt (UCR1_TXMPTYEN) in
imx_transmit_buffer() but not Transmit Complete Interrupt and so fails
to remove this irq source which prevents the DMA request to start and
completely locks up the system.
To prevent this lock-up also disable UCR4_TCEN when starting DMA and
expand the comment accordingly.
Fixes: 17b8f2a3fdca ("serial: imx: add support for half duplex rs485")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
---
drivers/tty/serial/imx.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 1d7ca382bc12..2a7311ad4788 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -436,9 +436,12 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
if (sport->dma_is_enabled) {
/*
- * We've just sent a X-char Ensure the TX DMA is enabled
- * and the TX IRQ is disabled.
- **/
+ * Ensure the TX IRQs are disabled when enabling DMA. Otherwise
+ * the triggering TX IRQ might prevent to start the DMA request.
+ */
+ temp = readl(sport->port.membase + UCR4);
+ if (temp & UCR4_TCEN)
+ writel(temp & ~UCR4_TCEN, sport->port.membase + UCR4);
temp = readl(sport->port.membase + UCR1);
temp &= ~UCR1_TXMPTYEN;
if (sport->dma_is_txing) {
--
2.15.1
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
