This is a note to let you know that I've just added the patch titled
tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A
to the 5.15-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-reduce-rx-watermark-to-0-on-ls.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4a80500d17d4872ca1c96bcfa8f52f3a59f413cf
Author: Robert Hodaszi <robert.hodaszi@xxxxxxxx>
Date: Fri Jun 9 14:13:34 2023 +0200
tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A
[ 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>
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 = {
