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Subject[PATCH] serial: imx: Raise TX trigger level to 8
Date
At the default TX trigger level of 2 in non-DMA mode (meaning that an
interrupt is generated when less than 2 characters are left in the
FIFO), we have observed frequent buffer underruns at 115200 Baud on an
i.MX8M Nano. This can cause communication issues if the receiving side
expects a continuous transfer.

Increasing the level to 8 makes the UART trigger an interrupt earlier,
giving the kernel enough time to refill the FIFO, at the cost of
triggering one interrupt per ~24 instead of ~30 bytes of transmitted
data (as the i.MX UART has a 32 byte FIFO).

Signed-off-by: Michael Krummsdorf <michael.krummsdorf@tq-group.com>
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
---
drivers/tty/serial/imx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 79f1503cd75b4..2eb22594960f3 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1305,7 +1305,7 @@ static void imx_uart_clear_rx_errors(struct imx_port *sport)

}

-#define TXTL_DEFAULT 2 /* reset default */
+#define TXTL_DEFAULT 8
#define RXTL_DEFAULT 8 /* 8 characters or aging timer */
#define TXTL_DMA 8 /* DMA burst setting */
#define RXTL_DMA 9 /* DMA burst setting */
--
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