RE: [PATCH v2] iio: filter: admv8818: Force initialization of SDO

[Miclaus, Antoniu]

> On Sat, 25 Jan 2025 14:54:44 +0000
> Sam Winchenbach <swinchenbach@xxxxxxxx> wrote:
> 
> > When a weak pull-up is present on the SDO line, regmap_update_bits fails
> > to write both the SOFTRESET and SDOACTIVE bits because it incorrectly
> > reads them as already set.
> 
> I can see this as a valid micro optimization but I'm struggling a bit
> on how you can use the device if the pull up is weak enough that
> you can't read data back from it. Does the reset in some way
> solve that?
> 
> Having asked for the fixes tag, I'm less sure on whether this is a fix.
> 
> Antoniu, I'd also like your input on this one!
> 
Indeed, this can be considered as a "bug". I had a look over the datasheet and the SDO line is disabled by default.

So the `update_bits` doesn't quite make sense in this scenario.

> >
> > Since the soft reset disables the SDO line, performing a
> > read-modify-write operation on ADI_SPI_CONFIG_A to enable the SDO line
> > doesn't make sense. This change directly writes to the register instead
> > of using regmap_update_bits.
> >
> > Fixes: f34fe888ad05 ("iio:filter:admv8818: add support for ADMV8818")
> >
> 
> No blank line here.  Fixes is part of the tags block that various scripts
> scan.
> 
> > Signed-off-by: Sam Winchenbach <swinchenbach@xxxxxxxx>
> > ---
> >  drivers/iio/filter/admv8818.c | 14 ++++----------
> >  1 file changed, 4 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/iio/filter/admv8818.c b/drivers/iio/filter/admv8818.c
> > index 195e58bc4..9cd1eee84 100644
> > --- a/drivers/iio/filter/admv8818.c
> > +++ b/drivers/iio/filter/admv8818.c
> > @@ -577,21 +577,15 @@ static int admv8818_init(struct admv8818_state
> *st)
> >  	struct spi_device *spi = st->spi;
> >  	unsigned int chip_id;
> >
> > -	ret = regmap_update_bits(st->regmap,
> ADMV8818_REG_SPI_CONFIG_A,
> > -				 ADMV8818_SOFTRESET_N_MSK |
> > -				 ADMV8818_SOFTRESET_MSK,
> > -
> FIELD_PREP(ADMV8818_SOFTRESET_N_MSK, 1) |
> > -				 FIELD_PREP(ADMV8818_SOFTRESET_MSK,
> 1));
> > +	ret = regmap_write(st->regmap, ADMV8818_REG_SPI_CONFIG_A,
> > +			   ADMV8818_SOFTRESET_N_MSK |
> ADMV8818_SOFTRESET_MSK);
> >  	if (ret) {
> >  		dev_err(&spi->dev, "ADMV8818 Soft Reset failed.\n");
> >  		return ret;
> >  	}
> >
> > -	ret = regmap_update_bits(st->regmap,
> ADMV8818_REG_SPI_CONFIG_A,
> > -				 ADMV8818_SDOACTIVE_N_MSK |
> > -				 ADMV8818_SDOACTIVE_MSK,
> > -
> FIELD_PREP(ADMV8818_SDOACTIVE_N_MSK, 1) |
> > -				 FIELD_PREP(ADMV8818_SDOACTIVE_MSK,
> 1));
> > +	ret = regmap_write(st->regmap, ADMV8818_REG_SPI_CONFIG_A,
> > +			   ADMV8818_SDOACTIVE_N_MSK |
> ADMV8818_SDOACTIVE_MSK);
> >  	if (ret) {
> >  		dev_err(&spi->dev, "ADMV8818 SDO Enable failed.\n");
> >  		return ret;