patch "staging: comedi: ni_mio_common: fix AO timer off-by-one regression" added to staging-linus

This is a note to let you know that I've just added the patch titled

staging: comedi: ni_mio_common: fix AO timer off-by-one regression

to my staging git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Ian Abbott <[email protected]>
Date: Fri, 30 Jun 2017 12:02:18 +0100
Subject: staging: comedi: ni_mio_common: fix AO timer off-by-one regression
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As reported by Éric Piel on the Comedi mailing list (see
<https://groups.google.com/forum/#!topic/comedi_list/ueZiR7vTLOU/discussion>),
the analog output asynchronous commands are running too fast with a period 50 ns shorter than it should be. This affects all boards with AO command support that are supported by the "ni_pcimio", "ni_atmio", and "ni_mio_cs" drivers.

This is a regression bug introduced by commit 080e6795cba3 ("staging:
comedi: ni_mio_common: Cleans up/clarifies ni_ao_cmd"), specifically, this line in ni_ao_cmd_set_update():

		/* following line: N-1 per STC */
		ni_stc_writel(dev, trigvar - 1, NISTC_AO_UI_LOADA_REG);

The trigvar variable value comes from a call to ni_ns_to_timer() which converts a timer period in nanoseconds to a hardware divisor value. The function already reduces the divisor by 1 as required by the hardware, so the above line should not reduce it further by 1. Fix it by replacing trigvar by trigvar - 1 in the above line, and remove the misleading comment.

---
 drivers/staging/comedi/drivers/ni_mio_common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index b2e382888981..2f7bfc1c59e5 100644
@@ -3116,8 +3116,7 @@ static void ni_ao_cmd_set_update(struct comedi_device *dev,
 		/* following line: 2-1 per STC */
 		ni_stc_writel(dev, 1, NISTC_AO_UI_LOADA_REG);
 		ni_stc_writew(dev, NISTC_AO_CMD1_UI_LOAD, NISTC_AO_CMD1_REG);
-		/* following line: N-1 per STC */
-		ni_stc_writel(dev, trigvar - 1, NISTC_AO_UI_LOADA_REG);
+		ni_stc_writel(dev, trigvar, NISTC_AO_UI_LOADA_REG);
 	} else { /* TRIG_EXT */
 		/* FIXME:  assert scan_begin_arg != 0, ret failure otherwise */
 		devpriv->ao_cmd2  |= NISTC_AO_CMD2_BC_GATE_ENA;

2.13.3