[PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[Robert Hodaszi]

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.

Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com>
---
 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 7486a2b8556c..7fd30fcc10c6 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -310,7 +310,7 @@ 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 = {
-- 
2.34.1

Re: [PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[Greg KH]

On Thu, Jun 08, 2023 at 01:19:27PM +0200, Robert Hodaszi wrote:
> 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.
> 
> Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com>

What commit id does this fix?  Should it go to stable releases?

thanks,

greg k-h

Re: [PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[Robert Hodaszi]

On 2023. 06. 08. 13:52, Greg KH wrote:
> What commit id does this fix?  Should it go to stable releases?
>
> thanks,
>
> greg k-h
Basically this one caused the issue on my unit:

    9ad9df8447547febe9dd09b040f4528a09e495f0

Check this discussion for more info:

    https://www.spinics.net/lists/linux-serial/msg54555.html

Yes, I think, it should go to stable.

Thank,
Robert

Re: [PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[Ilpo Järvinen]

On Thu, 8 Jun 2023, Robert Hodaszi wrote:

> On 2023. 06. 08. 13:52, Greg KH wrote:
> > What commit id does this fix?  Should it go to stable releases?
> >
> > thanks,
> >
> > greg k-h
> Basically this one caused the issue on my unit:
> 
>     9ad9df8447547febe9dd09b040f4528a09e495f0
> 
> Check this discussion for more info:
> 
>     https://www.spinics.net/lists/linux-serial/msg54555.html
> 
> Yes, I think, it should go to stable.

Please provide a new version of the patch with Fixes + Link tags then
(for Link tag, prefer to use lore archive links).

You can find out the correct format of those tags from the information 
under Documentation/process/.

-- 
 i.

Re: [PATCH] tty: serial: fsl_lpuart: reduce RX watermark to 0 on LS1028A

[Robert Hodaszi]

On 2023. 06. 08. 17:56, Ilpo Järvinen wrote:
> Please provide a new version of the patch with Fixes + Link tags then
> (for Link tag, prefer to use lore archive links).
>
> You can find out the correct format of those tags from the information
> under Documentation/process/.
>
> --
>  i.
>
Hi,

Thanks, done! Hope I added correctly.

Robert