linux-kernel - Re: [PATCH v4 6/7] gpio: exar: switch to using regmap

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Date:   Tue, 10 Nov 2020 16:12:38 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        David Laight <David.Laight@...lab.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v4 6/7] gpio: exar: switch to using regmap

On Tue, Nov 10, 2020 at 4:09 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Tue, Nov 10, 2020 at 05:04:47PM +0200, Andy Shevchenko wrote:
> > On Tue, Nov 10, 2020 at 03:55:51PM +0100, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > >
> > > We can simplify the code in gpio-exar by using regmap. This allows us to
> > > drop the mutex (regmap provides its own locking) and we can also reuse
> > > regmap's bit operations instead of implementing our own update function.
> >
> > ...
> >
> > > +static const struct regmap_config exar_regmap_config = {
> > > +   .name           = "exar-gpio",
> > > +   .reg_bits       = 16,
> >
> > As per previous version comment.
> >
> > Hold on, the registers are 16-bit wide, but their halves are sparsed!
> > So, I guess 8 and 8 with helpers to get hi and lo parts are essential.
> >
> >
> > TABLE 5: DEVICE CONFIGURATION REGISTERS SHOWN IN BYTE ALIGNMENT
> >
> > > +   .val_bits       = 8,
> > > +};
> >
> > This is basically represents two banks out of 6 8-bit registers each.
>
> ...which makes me wonder if gpio-regmap can be utilized here...
>

But the address width won't affect the actuall accessing of 8 bits
registers in an mmio regmap. Internally the mmio regmap does pretty
much the same thing the previous driver did: call readb()/writeb() on
8-bit "chunks" of the banks.

Bartosz