linux-kernel - Re: [PATCH] Revert "serial: 8250: Fix clearing FIFOs in RS485 mode again"

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Date:   Sun, 16 Dec 2018 22:24:13 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
CC:     Marek Vasut <marex@...x.de>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Burton <pburton@...ecomp.com>,
        Daniel Jedrychowski <avistel@...il.com>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: Re: [PATCH] Revert "serial: 8250: Fix clearing FIFOs in RS485 mode
 again"

Hi Ezequiel,

On Sun, Dec 16, 2018 at 06:52:53PM -0300, Ezequiel Garcia wrote:
> diff --git a/drivers/tty/serial/8250/8250_port.c
> b/drivers/tty/serial/8250/8250_port.c
> index c39482b96111..fac19cbc51d1 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2209,10 +2209,11 @@ int serial8250_do_startup(struct uart_port *port)
>         /*
>          * Clear the FIFO buffers and disable them.
>          * (they will be reenabled in set_termios())
>          */
>         serial8250_clear_fifos(up);
> +       serial_out(up, UART_FCR, 0);
> 
>         /*
>          * Clear the interrupt registers.
>          */
>         serial_port_in(port, UART_LSR);
> 

This helps, but it only addresses one part of one of the 4 reasons I
listed as motivation for my revert. For example serial8250_do_shutdown()
also clearly intends to disable the FIFOs.

Thanks,
    Paul