linux-kernel - Re: [PATCH 1/2] iio: adc: stx104: Implement and utilize register structures

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Date:   Wed, 15 Jun 2022 14:43:27 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     William Breathitt Gray <william.gray@...aro.org>,
        Mark Brown <broonie@...nel.org>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] iio: adc: stx104: Implement and utilize register structures

On Wed, Jun 15, 2022 at 2:19 PM William Breathitt Gray
<william.gray@...aro.org> wrote:
> On Wed, Jun 15, 2022 at 02:00:26PM +0200, Andy Shevchenko wrote:
> > On Wed, Jun 15, 2022 at 1:55 PM William Breathitt Gray
> > <william.gray@...aro.org> wrote:
> > > On Wed, Jun 15, 2022 at 11:44:54AM +0200, Andy Shevchenko wrote:
> > > > On Mon, Jun 6, 2022 at 4:27 PM William Breathitt Gray
> > > > <william.gray@...aro.org> wrote:
> > > > >
> > > > > Reduce magic numbers and improve code readability by implementing and
> > > > > utilizing named register data structures.
> > > >
> > > > Can we consider using regmap APIs instead?
> >
> > > The regmap API may be more appropriate here. I'll investigate and see if
> > > I can convert this over to it.
> >
> > I just realized that this driver is for the old PC104 (like?) hardware
> > that most likely uses IO ports, I don't remember if we have support
> > for IO ports in regmap (MMIO -- yes for sure).

> Hmm, I don't see IO ports mentioned in include/linux/regmap.h, so I
> don't think the regmap API directly supports it (maybe someone familiar
> with regmap knows). Although we do get a virtual mapping cookie via
> ioport_map() in this driver, I don't know if we can pass that to the
> regmap functions and have it actually work.

The problem is with accessors which are inconsistent in regmap MMIO
implementation. I think it should be converted to use
ioreadXX()/iowriteXX() in all cases (currently only BE cases use
them). Another variant is to provide read*_be() / write*_be() for all
architectures, replace corresponding ops in regmap MMIO and introduce
regmap IO with inX()/outX. The former seems to me the best option,
while the latter is cleaner.

+Cc: Mark if he knows more about this.

-- 
With Best Regards,
Andy Shevchenko