linux-kernel - [PATCH 3.16 12/87] serial: sh-sci: disable DMA for uart

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Message-ID: <lsq.1570043211.904590300@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Michael Rodin" <mrodin@...adit-jv.com>,
        "Wolfram Sang" <wsa+renesas@...g-engineering.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "George G. Davis" <george_davis@...tor.com>,
        "Geert Uytterhoeven" <geert+renesas@...der.be>,
        "Simon Horman" <horms+renesas@...ge.net.au>,
        "Eugeniu Rosca" <erosca@...adit-jv.com>
Subject: [PATCH 3.16 12/87] serial: sh-sci: disable DMA for uart_console

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "George G. Davis" <george_davis@...tor.com>

commit 099506cbbc79c0bd52b19cb6b930f256dabc3950 upstream.

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.

Reported-by: Michael Rodin <mrodin@...adit-jv.com>
Link: https://patchwork.kernel.org/patch/10929511/
Tested-by: Eugeniu Rosca <erosca@...adit-jv.com>
Reviewed-by: Simon Horman <horms+renesas@...ge.net.au>
Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
Signed-off-by: George G. Davis <george_davis@...tor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/serial/sh-sci.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1600,6 +1600,13 @@ static void sci_request_dma(struct uart_
 
 	dev_dbg(port->dev, "%s: port %d\n", __func__, port->line);
 
+	/*
+	 * DMA on console may interfere with Kernel log messages which use
+	 * plain putchar(). So, simply don't use it with a console.
+	 */
+	if (uart_console(port))
+		return;
+
 	if (s->cfg->dma_slave_tx <= 0 || s->cfg->dma_slave_rx <= 0)
 		return;