RE: [PATCH 5/6] tty: serial: fsl_lpuart: set RTS watermark for lpuart

[Sherry Sun]

> -----Original Message-----
> From: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
> Sent: 2023年2月2日 15:14
> To: Sherry Sun <sherry.sun@xxxxxxx>
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; jirislaby@xxxxxxxxxx; linux-
> serial@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-
> imx@xxxxxxx>
> Subject: Re: [PATCH 5/6] tty: serial: fsl_lpuart: set RTS watermark for lpuart
> 
> Am Montag, 30. Januar 2023, 07:44:48 CET schrieb Sherry Sun:
> > Add RTS watermark support for LPUART. The RX RTS_B output negates
> when
> > the number of empty words in the receive FIFO is greater or equal to
> > RTSWATER. Here set the RTSWATER to half of the rxfifo_size.
> >
> > Signed-off-by: Sherry Sun <sherry.sun@xxxxxxx>
> > ---
> >  drivers/tty/serial/fsl_lpuart.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c index 2789749d3d0d..c35e49a09bcc
> > 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -201,6 +201,7 @@
> >  #define UARTDATA_MASK		0x3ff
> >
> >  #define UARTMODIR_IREN		0x00020000
> > +#define UARTMODIR_RTSWATER	GENMASK(10, 8)
> >  #define UARTMODIR_TXCTSSRC	0x00000020
> >  #define UARTMODIR_TXCTSC	0x00000010
> >  #define UARTMODIR_RXRTSE	0x00000008
> > @@ -1573,6 +1574,13 @@ static void lpuart32_setup_watermark(struct
> > lpuart_port *sport) (0x0 << UARTWATER_TXWATER_OFF);
> >  	lpuart32_write(&sport->port, val, UARTWATER);
> >
> > +	/* set RTS watermark */
> > +	if (!uart_console(&sport->port)) {
> > +		val = lpuart32_read(&sport->port, UARTMODIR);
> > +		val |= FIELD_PREP(UARTMODIR_RTSWATER, sport-
> >rxfifo_size
> >> 1);
> > +		lpuart32_write(&sport->port, val, UARTMODIR);
> 
> On LS1021A these bits are reserved (please refer to QorIQ LS1021A Reference
> manual Rev 3.1 02/2020 section 27.3.6). Is it okay to write to them?
> 
Hi Alexander,

I checked the LS1021A RM, writing the reserved register bits have no impact, so it is okay here.
Also, nxp local linux repo add this patch for a long time, all imx and layerscape boards work well with this patch.

Best Regards
Sherry