linux-kernel - Re: [PATCH 5/6] tty: serial: fsl_lpuart: set RTS watermark for lpuart

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Date:   Thu, 02 Feb 2023 08:14:09 +0100
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     Sherry Sun <sherry.sun@....com>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
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@....com>
> ---
>  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?

Best regards
Alexander

> +	}
> +
>  	/* Restore cr2 */
>  	lpuart32_write(&sport->port, ctrl_saved, UARTCTRL);
>  }