linux-kernel - Re: [PATCH v4 4/5] serial: 8250: Also set sticky MCR bits in console restoration

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Date:   Mon, 18 Apr 2022 15:19:19 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stable <stable@...r.kernel.org>
Subject: Re: [PATCH v4 4/5] serial: 8250: Also set sticky MCR bits in console restoration

On Mon, Apr 18, 2022 at 2:02 AM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
> Sticky MCR bits are lost in console restoration if console suspending
> has been disabled.  This currently affects the AFE bit, which works in
> combination with RTS which we set, so we want to make sure the UART
> retains control of its FIFO where previously requested.  Also specific
> drivers may need other bits in the future.

Since it's a fix it should be moved to the beginning of the series.

Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>

> Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
> Fixes: 4516d50aabed ("serial: 8250: Use canary to restart console after suspend")
> Cc: stable@...r.kernel.org # v4.0+
> ---
> New change in v4, factored out from 5/5.
> ---
>  drivers/tty/serial/8250/8250_port.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> linux-serial-8250-mcr-restore.diff
> Index: linux-macro/drivers/tty/serial/8250/8250_port.c
> ===================================================================
> --- linux-macro.orig/drivers/tty/serial/8250/8250_port.c
> +++ linux-macro/drivers/tty/serial/8250/8250_port.c
> @@ -3308,7 +3308,7 @@ static void serial8250_console_restore(s
>
>         serial8250_set_divisor(port, baud, quot, frac);
>         serial_port_out(port, UART_LCR, up->lcr);
> -       serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS);
> +       serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
>  }
>
>  /*



-- 
With Best Regards,
Andy Shevchenko