linux-kernel - [PATCH 3.12 043/111] staging: comedi: ni_daq

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Message-Id: <089768acf22bb5a9d5a255413e5fdac0ad15c6ea.1403512281.git.jslaby@suse.cz>
Date:	Mon, 23 Jun 2014 10:31:18 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Ian Abbott <abbotti@....co.uk>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 043/111] staging: comedi: ni_daq_700: add mux settling delay

From: Ian Abbott <abbotti@....co.uk>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit ffed54dced86723f352323f15789d9ad6bee25e1 upstream.

I got a patch from the original author, Fred Brooks, to add a small
settling delay after setting the AI channel multiplexor.  The lack of
delay resulted in unstable or scrambled data on faster processors.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
Reported-by: Fred Brooks <nsaspook@...spook.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/staging/comedi/drivers/ni_daq_700.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/comedi/drivers/ni_daq_700.c b/drivers/staging/comedi/drivers/ni_daq_700.c
index 404f83de276d..40ca2be1d9d2 100644
--- a/drivers/staging/comedi/drivers/ni_daq_700.c
+++ b/drivers/staging/comedi/drivers/ni_daq_700.c
@@ -118,6 +118,8 @@ static int daq700_ai_rinsn(struct comedi_device *dev,
 	/* write channel to multiplexer */
 	/* set mask scan bit high to disable scanning */
 	outb(chan | 0x80, dev->iobase + CMD_R1);
+	/* mux needs 2us to really settle [Fred Brooks]. */
+	udelay(2);
 
 	/* convert n samples */
 	for (n = 0; n < insn->n; n++) {
-- 
2.0.0

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