[PATCH 36/36] staging: comedi: cb_pcidas: cleanup dac08_write()

[PATCH 36/36] staging: comedi: cb_pcidas: cleanup dac08_write()

[H Hartley Sweeten]

Reverse the logic of the test against the cached value so that
the function only has one exit point.

Make the logic of the dac write a bit clearer by create a local
variable for the address used in the outw() calls and masking the
value to write and setting the enable bits before doing the outw()
calls. Add a comment just to make sure it's clear.

Also, add a comment about the 'return 1;'.  This should be
insn->n which is the number of data parameters used to do the
dac08_write_insn() but the insn is not a parameter to this
function.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/staging/comedi/drivers/cb_pcidas.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/staging/comedi/drivers/cb_pcidas.c b/drivers/staging/comedi/drivers/cb_pcidas.c
index 1479325..3ba75af 100644
--- a/drivers/staging/comedi/drivers/cb_pcidas.c
+++ b/drivers/staging/comedi/drivers/cb_pcidas.c
@@ -662,23 +662,25 @@ static int caldac_read_insn(struct comedi_device *dev,
 static int dac08_write(struct comedi_device *dev, unsigned int value)
 {
 	struct cb_pcidas_private *devpriv = dev->private;
+	unsigned long cal_reg;
 
-	if (devpriv->dac08_value == value)
-		return 1;
+	if (devpriv->dac08_value != value) {
+		devpriv->dac08_value = value;
 
-	devpriv->dac08_value = value;
+		cal_reg = devpriv->control_status + CALIBRATION_REG;
 
-	outw(cal_enable_bits(dev) | (value & 0xff),
-	     devpriv->control_status + CALIBRATION_REG);
-	udelay(1);
-	outw(cal_enable_bits(dev) | SELECT_DAC08_BIT | (value & 0xff),
-	     devpriv->control_status + CALIBRATION_REG);
-	udelay(1);
-	outw(cal_enable_bits(dev) | (value & 0xff),
-	     devpriv->control_status + CALIBRATION_REG);
-	udelay(1);
+		value &= 0xff;
+		value |= cal_enable_bits(dev);
 
-	return 1;
+		/* latch the new value into the caldac */
+		outw(value, cal_reg);
+		udelay(1);
+		outw(value | SELECT_DAC08_BIT, cal_reg);
+		udelay(1);
+		outw(value, cal_reg);
+		udelay(1);
+	}
+	return 1;	/* insn->n */
 }
 
 static int dac08_write_insn(struct comedi_device *dev,
-- 
1.7.11

Re: [PATCH 36/36] staging: comedi: cb_pcidas: cleanup dac08_write()

[Ian Abbott]

On 2012-06-27 02:12, H Hartley Sweeten wrote:
> Reverse the logic of the test against the cached value so that
> the function only has one exit point.
>
> Make the logic of the dac write a bit clearer by create a local
> variable for the address used in the outw() calls and masking the
> value to write and setting the enable bits before doing the outw()
> calls. Add a comment just to make sure it's clear.
>
> Also, add a comment about the 'return 1;'.  This should be
> insn->n which is the number of data parameters used to do the
> dac08_write_insn() but the insn is not a parameter to this
> function.

It's probably better to make dac08_write() return void and return 1 in 
dac08_write_insn().

Actually, I think dac08_write_insn() ought to call dac08_write() in a 
loop, iterating over data[] and return insn->n.  That's what the 
INSN_WRITE instruction is meant to do although it's not implemented all 
that consistently by the drivers.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-