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

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Date:   Sun, 16 Dec 2018 18:52:53 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Marek Vasut <marex@...x.de>
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 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);


-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar