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

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Message-ID: <CAMpxmJV4hsV34YS0Ez9_GsnBakXGgr3NTu8oBd+3Apg+921aRQ@mail.gmail.com>
Date:   Tue, 10 Nov 2020 17:36:48 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        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>
Subject: Re: [PATCH v4 6/7] gpio: exar: switch to using regmap

On Tue, Nov 10, 2020 at 5:17 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Tue, Nov 10, 2020 at 04:12:38PM +0100, Bartosz Golaszewski wrote:
> > 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.
>
> It will affect reg dump in debugfs. I would really narrow down the register
> address space in the config, otherwise that debugfs facility will screw up a
> lot of things.
>
> So, and to be on pedantic side...
>
> "The Device Configuration Registers and the two individual UART Configuration
> Registers of the XR17V352 occupy 2K of PCI bus memory address space."
>
> 11 seems the correct value for the address width.
>

I take it as a typo and assume you meant 16. So the patch should be
correct and your review tag is good to go?

Bartosz