Linux-Renesas-SoC Archive on
 help / color / Atom feed
* [PATCH v3] serial: sh-sci: disable DMA for uart_console
@ 2019-05-15  3:29 George G. Davis
  0 siblings, 0 replies; only message in thread
From: George G. Davis @ 2019-05-15  3:29 UTC (permalink / raw)
  To: Eugeniu Rosca, Geert Uytterhoeven, Simon Horman, Wolfram Sang,
	Greg Kroah-Hartman, Jiri Slaby, open list:SERIAL DRIVERS,
	open list
  Cc: Chris Brandt, Ulrich Hecht, Andy Lowe, Linux-Renesas,
	Rob Herring, Mark Rutland, George G. Davis, stable

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 <>
Tested-by: Eugeniu Rosca <>
Reviewed-by: Simon Horman <>
Reviewed-by: Wolfram Sang <>
Reviewed-by: Geert Uytterhoeven <>
Signed-off-by: George G. Davis <>
v2: Clarify comment regarding DMA support on kernel console,
    add {Tested,Reviewed}-by:, and Cc: linux-stable lines.
v3: Change Fixes: reference to Link: reference and add another Reviewed-by.
 drivers/tty/serial/sh-sci.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 3cd139752d3f..abc705716aa0 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1557,6 +1557,13 @@ static void sci_request_dma(struct uart_port *port)
 	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 (!port->dev->of_node)

^ permalink raw reply	[flat|nested] only message in thread

only message in thread, back to index

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-15  3:29 [PATCH v3] serial: sh-sci: disable DMA for uart_console George G. Davis

Linux-Renesas-SoC Archive on

Archives are clonable:
	git clone --mirror linux-renesas-soc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-renesas-soc linux-renesas-soc/ \
	public-inbox-index linux-renesas-soc

Newsgroup available over NNTP:

AGPL code for this site: git clone public-inbox