linux-kernel - Re: [PATCH v2 1/4] iio: adc: ad7949: define and use bitfield names

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Message-Id: <CCPNZV2YBJBG.3VSIFN36ZOD4W@shaak>
Date:   Sat, 10 Jul 2021 14:17:22 -0400
From:   "Liam Beguin" <liambeguin@...il.com>
To:     "Jonathan Cameron" <jic23@...nel.org>
Cc:     <lars@...afoo.de>, <Michael.Hennerich@...log.com>,
        <charles-antoine.couret@...ensium.com>, <Nuno.Sa@...log.com>,
        <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <robh+dt@...nel.org>
Subject: Re: [PATCH v2 1/4] iio: adc: ad7949: define and use bitfield names

On Sat Jul 10, 2021 at 12:08 PM EDT, Jonathan Cameron wrote:
> On Fri, 9 Jul 2021 11:58:53 -0400
> Liam Beguin <liambeguin@...il.com> wrote:
>
> > From: Liam Beguin <lvb@...hos.com>
> > 
> > Replace raw configuration register values by using FIELD_PREP and
> > defines to improve readability.
> > 
> > Signed-off-by: Liam Beguin <lvb@...hos.com>

Hi Jonathan,

>
> Ideally fixes should come before any refactors / cleanups like this one.
> That reduces the burden if people want to backport them.
>
> In this particular case I'm guessing no one ran into the issues the
> following patches deal with so we can just take these in the order
> you have here.
>

Understood, I will follow that guideline next time.

> Otherwise, good cleanup. A few minor comments inline, mostly as a result
> of some less than ideal name choices on the datasheet.
>
> > ---
> >  drivers/iio/adc/ad7949.c | 38 +++++++++++++++++++++++++++++++-------
> >  1 file changed, 31 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > index 1b4b3203e428..93aacf4f680b 100644
> > --- a/drivers/iio/adc/ad7949.c
> > +++ b/drivers/iio/adc/ad7949.c
> > @@ -12,12 +12,27 @@
> >  #include <linux/regulator/consumer.h>
> >  #include <linux/spi/spi.h>
> >  
> > -#define AD7949_MASK_CHANNEL_SEL		GENMASK(9, 7)
> >  #define AD7949_MASK_TOTAL		GENMASK(13, 0)
> > -#define AD7949_OFFSET_CHANNEL_SEL	7
> > -#define AD7949_CFG_READ_BACK		0x1
> >  #define AD7949_CFG_REG_SIZE_BITS	14
> >  
> > +#define AD7949_CFG_BIT_CFG		BIT(13)
>
> Even though that's the name on the datasheet it is silly!

Agreed, datasheet register and bitfield names aren't always great :-/

>
> I would have just one define called
> AD7949_CFG_VAL_OVERWRITE BIT(13)
>
> It's common to do that for single flags where
> FIELD_PREP(AD7949_CFG_VAL_OVERWRITE, 1) for example has an
> obvious meaning for the 1.
>

Sounds good, I'll fix these with your recommendation.

> > +#define AD7949_CFG_VAL_CFG_OVERWRITE		1
> > +#define AD7949_CFG_VAL_CFG_KEEP			0
> > +#define AD7949_CFG_BIT_INCC		GENMASK(12, 10)
> > +#define AD7949_CFG_VAL_INCC_UNIPOLAR_GND	7
> > +#define AD7949_CFG_VAL_INCC_UNIPOLAR_COMM	6
> > +#define AD7949_CFG_VAL_INCC_UNIPOLAR_DIFF	4
> > +#define AD7949_CFG_VAL_INCC_TEMP		3
> > +#define AD7949_CFG_VAL_INCC_BIPOLAR		2
> > +#define AD7949_CFG_VAL_INCC_BIPOLAR_DIFF	0
> > +#define AD7949_CFG_BIT_INX		GENMASK(9, 7)
>
> This is rather non obvious abbreviation. _INx would be clearer
> perhaps, but then we'd get someone fixing the camel case...
> Given it would be good to match the datasheet, keep the name
> but add a comment to say this is the input channel select.
>

I agree! While I'm at it, I might as well add comments for INCC and
others that aren't so abvious.

Thanks,
Liam

> > +#define AD7949_CFG_BIT_BW		BIT(6)
>
> As above, I'd suggest just defining AD7949_CFG_VAL_BW_FULL BIT(6)
> then it's either full or not depending on a 0 or 1 write.
>
> > +#define AD7949_CFG_VAL_BW_FULL			1
> > +#define AD7949_CFG_VAL_BW_QUARTER		0
> > +#define AD7949_CFG_BIT_REF		GENMASK(5, 3)
> > +#define AD7949_CFG_BIT_SEQ		GENMASK(2, 1)
> > +#define AD7949_CFG_BIT_RBN		BIT(0)
> > +
> >  enum {
> >  	ID_AD7949 = 0,
> >  	ID_AD7682,
> > @@ -109,8 +124,8 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
> >  	 */
> >  	for (i = 0; i < 2; i++) {
> >  		ret = ad7949_spi_write_cfg(ad7949_adc,
> > -					   channel << AD7949_OFFSET_CHANNEL_SEL,
> > -					   AD7949_MASK_CHANNEL_SEL);
> > +					   FIELD_PREP(AD7949_CFG_BIT_INX, channel),
> > +					   AD7949_CFG_BIT_INX);
> >  		if (ret)
> >  			return ret;
> >  		if (channel == ad7949_adc->current_channel)
> > @@ -214,10 +229,19 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
> >  {
> >  	int ret;
> >  	int val;
> > +	u16 cfg;
> >  
> > -	/* Sequencer disabled, CFG readback disabled, IN0 as default channel */
> >  	ad7949_adc->current_channel = 0;
> > -	ret = ad7949_spi_write_cfg(ad7949_adc, 0x3C79, AD7949_MASK_TOTAL);
> > +
> > +	cfg = FIELD_PREP(AD7949_CFG_BIT_CFG, AD7949_CFG_VAL_CFG_OVERWRITE) |
> > +		FIELD_PREP(AD7949_CFG_BIT_INCC, AD7949_CFG_VAL_INCC_UNIPOLAR_GND) |
> > +		FIELD_PREP(AD7949_CFG_BIT_INX, ad7949_adc->current_channel) |
> > +		FIELD_PREP(AD7949_CFG_BIT_BW, AD7949_CFG_VAL_BW_FULL) |
> > +		FIELD_PREP(AD7949_CFG_BIT_REF, AD7949_REF_EXT_BUF) |
> > +		FIELD_PREP(AD7949_CFG_BIT_SEQ, 0x0) |
> > +		FIELD_PREP(AD7949_CFG_BIT_RBN, 1);
> > +
> > +	ret = ad7949_spi_write_cfg(ad7949_adc, cfg, AD7949_MASK_TOTAL);
> >  
> >  	/*
> >  	 * Do two dummy conversions to apply the first configuration setting.