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

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Date:   Sun, 16 Dec 2018 23:11:43 +0100
From:   Marek Vasut <marex@...x.de>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     Paul Burton <paul.burton@...s.com>,
        "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"

On 12/16/2018 10:52 PM, Ezequiel Garcia wrote:
> On Sun, 16 Dec 2018 at 18:45, Marek Vasut <marex@...x.de> wrote:
> [skips discussion]
>>
>>> Ultimately it's Greg's decision but it sounds like you're asking me to
>>> say it's OK to break the JZ4780 in a stable kernel with a patch that I
>>> think would be risky anyway, and I won't do that.
>>
>> I am saying this revert breaks AM335x, so this is a stalemate. I had a
>> discussion with Ezequiel (on CC) and he seems to have a different
>> smaller patch coming for this problem.
>>
> 
> Can you guys test this? Note that serial8250_do_startup has a comment
> stating clearly that it has the intention of disabling the FIFOs,
> so it seems this is the right thing to do.
> 
> Paul, this removes the garbage on my CI20 (rev.1)
> 
> 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);
> 
> 

On AM335x pocketbeagle
Tested-by: Marek Vasut <marex@...x.de>

-- 
Best regards,
Marek Vasut