From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH] serial: sh-sci: disable DMA for uart_console
Date: Mon, 13 May 2019 15:51:14 +0200
Message-ID: <20190513135114.GA20443@kunai>
References: <20190506194233.GA32430@vmlxhi-102.adit-jv.com>
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To: "George G. Davis" <ggdavisiv@gmail.com>
Cc: Eugeniu Rosca <erosca@de.adit-jv.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.com>, "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>, open list <linux-kernel@vger.kernel.org>, Simon Horman <horms+renesas@verge.net.au>, Chris Brandt <chris.brandt@renesas.com>, Wolfram Sang <wsa+renesas@sang-engineering.com>, Ulrich Hecht <ulrich.hecht+renesas@gmail.com>, Andy Lowe <andy_lowe@mentor.com>, Linux-Renesas <linux-renesas-soc@vger.kernel.org>, OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetree@vger.kernel.org>, Magnus Damm <magnus.damm@gmail.com>, Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>, "George G. Davis" <george_davis@mentor.com>
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On Thu, May 09, 2019 at 10:43:30AM -0400, George G. Davis wrote:
> As noted in commit 84b40e3b57ee ("serial: 8250: omap: Disable DMA for
> console UART"), UART console lines use low-level PIO only access functions
> which will conflict with use of the line when DMA is enabled, e.g. when
> the console line is also used for systemd messages. So disable DMA
> support for UART console lines.
>=20
> Fixes: https://patchwork.kernel.org/patch/10929511/
> Reported-by: Michael Rodin <mrodin@de.adit-jv.com>
> Cc: Eugeniu Rosca <erosca@de.adit-jv.com>
> Signed-off-by: George G. Davis <george_davis@mentor.com>
> ---
>  drivers/tty/serial/sh-sci.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 3cd139752d3f..885b56b1d4e4 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -1557,6 +1557,9 @@ static void sci_request_dma(struct uart_port *port)
> =20
>  	dev_dbg(port->dev, "%s: port %d\n", __func__, port->line);
> =20
> +	if (uart_console(port))
> +		return; /* Cannot use DMA on console */

Minor nit: maybe the comment can be made more specific?

/*
 * DMA on console may interfere with Kernel log messages which use
 * plain putchar(). So, simply don't use it with a console.
 */

Other than that:

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Much better than dropping the properties, as Geert noted.


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