linux-kernel - Re: [PATCH v3 1/2] iio: addac: stx104: Migrate to the regmap API

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Date:   Sun, 2 Apr 2023 10:51:19 -0400
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] iio: addac: stx104: Migrate to the regmap API

On Sun, Apr 02, 2023 at 05:46:57PM +0100, Jonathan Cameron wrote:
> 
> > > > +	.wr_table = &aio_ctl_wr_table,
> > > > +	.rd_table = &aio_ctl_rd_table,
> > > > +	.volatile_table = &aio_ctl_volatile_table,
> > > > +	.cache_type = REGCACHE_FLAT,
> > > > +};  
> > > 
> > > Do we need regmap lock?  
> > 
> > I think the regmap lock is opt-out, so I don't think we need to set an
> > custom lock callback for the regmaps in this driver.
> > 
> > Jonathan, do read_raw() and write_raw() require explicit locking?
> 
> The don't provide their own locking.  Depending on the access pattern the
> underlying bus locking may be sufficient.  If you have read modify write
> cycles though you'll want locking at the appropriate level for that
> which might well be at the level of regmap.
> 
> Jonathan

If read_raw() can be called concurrently multiple times then we risk
changing the ADC channel while the analog-to-digital conversion is in
progress, thus resulting in an incorrect reported value. Looks like
we'll need an explicit lock for this after all, so I'll create a
precursor patch addressing that.

William Breathitt Gray

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