From: Robert Hodaszi <robert.hodaszi@xxxxxxxx> [ Upstream commit a82c3df955f8c1c726e4976527aa6ae924a67dd9 ] LS1028A is using DMA with LPUART. Having RX watermark set to 1, means DMA transactions are started only after receiving the second character. On other platforms with newer LPUART IP, Receiver Idle Empty function initiates the DMA request after the receiver is idling for 4 characters. But this feature is missing on LS1028A, which is causing a 1-character delay in the RX direction on this platform. Set RX watermark to 0 to initiate RX DMA after each character. Link: https://lore.kernel.org/linux-serial/20230607103459.1222426-1-robert.hodaszi@xxxxxxxx/ Fixes: 9ad9df844754 ("tty: serial: fsl_lpuart: Fix the wrong RXWATER setting for rx dma case") Cc: stable <stable@xxxxxxxxxx> Signed-off-by: Robert Hodaszi <robert.hodaszi@xxxxxxxx> Message-ID: <20230609121334.1878626-1-robert.hodaszi@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/tty/serial/fsl_lpuart.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 380d9237989b2..74b445fb065bd 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -300,7 +300,7 @@ static const struct lpuart_soc_data ls1021a_data = { static const struct lpuart_soc_data ls1028a_data = { .devtype = LS1028A_LPUART, .iotype = UPIO_MEM32, - .rx_watermark = 1, + .rx_watermark = 0, }; static struct lpuart_soc_data imx7ulp_data = { -- 2.40.1
