linux-kernel - [PATCH 3.14 48/78] staging: comedi: ni_daq

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Message-Id: <20140609224814.903110023@linuxfoundation.org>
Date:	Mon,  9 Jun 2014 15:48:28 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Ian Abbott <abbotti@....co.uk>,
	Fred Brooks <nsaspook@...spook.com>
Subject: [PATCH 3.14 48/78] staging: comedi: ni_daq_700: add mux settling delay

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

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

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

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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/staging/comedi/drivers/ni_daq_700.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/staging/comedi/drivers/ni_daq_700.c
+++ b/drivers/staging/comedi/drivers/ni_daq_700.c
@@ -122,6 +122,8 @@ static int daq700_ai_rinsn(struct comedi
 	/* 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++) {


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