linux-kernel - Re: [PATCH] tty: serial: imx: disable UCR4_OREN in .stop

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Message-ID: <20211123075122.2cwhrdwrsyjgebnk@pengutronix.de>
Date:   Tue, 23 Nov 2021 08:51:22 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
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] tty: serial: imx: disable UCR4_OREN in .stop_rx()

On Tue, Nov 23, 2021 at 03:04:37PM +0800, Sherry Sun wrote:
> From: Fugang Duan <fugang.duan@....com>
> 
> Disable UCR4_OREN bit in .stop_rx() to avoid endless
> interrupt happen while tty port is closing.
> 
> Signed-off-by: Fugang Duan <fugang.duan@....com>
> Signed-off-by: Sherry Sun <sherry.sun@....com>
> ---
>  drivers/tty/serial/imx.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index fb75e3e0d828..9ecaf051249d 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -486,18 +486,21 @@ static void imx_uart_stop_tx(struct uart_port *port)
>  static void imx_uart_stop_rx(struct uart_port *port)
>  {
>  	struct imx_port *sport = (struct imx_port *)port;
> -	u32 ucr1, ucr2;
> +	u32 ucr1, ucr2, ucr4;
>  
>  	ucr1 = imx_uart_readl(sport, UCR1);
>  	ucr2 = imx_uart_readl(sport, UCR2);
> +	ucr4 = imx_uart_readl(sport, UCR4);
>  
>  	if (sport->dma_is_enabled) {
>  		ucr1 &= ~(UCR1_RXDMAEN | UCR1_ATDMAEN);
>  	} else {
>  		ucr1 &= ~UCR1_RRDYEN;
>  		ucr2 &= ~UCR2_ATEN;
> +		ucr4 &= ~UCR4_OREN;
>  	}
>  	imx_uart_writel(sport, ucr1, UCR1);
> +	imx_uart_writel(sport, ucr4, UCR4);

I don't understand this yet, but I guess this is just a matter of
improving the commit log. How does the endless irq happen?

... some time later after thinking and reading the driver source ...

Hmm, when the OR event is triggered the handler does

	imx_uart_writel(sport, USR2_ORE, USR2);

and so clears the event. I would expect that this should be good enough
to prevent an irq storm even if the receiver is disabled. Doesn't acking
work with the receiver disabled?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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