linux-kernel - Re: [PATCH v4 1/2] gpio: Add support for IDT 79RC3243x GPIO controller

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Date:   Wed, 28 Apr 2021 17:07:55 +0200
From:   Michael Walle <michael@...le.cc>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v4 1/2] gpio: Add support for IDT 79RC3243x GPIO
 controller

Am 2021-04-28 17:02, schrieb Andy Shevchenko:
> On Wed, Apr 28, 2021 at 5:48 PM Michael Walle <michael@...le.cc> wrote:
>> 
>> [Adding Mark here, too]
>> 
>> Am 2021-04-28 16:32, schrieb Andy Shevchenko:
>> > On Wed, Apr 28, 2021 at 5:04 PM Michael Walle <michael@...le.cc> wrote:
>> >> Am 2021-04-28 15:44, schrieb Andy Shevchenko:
>> >> > On Wed, Apr 28, 2021 at 2:57 PM Michael Walle <michael@...le.cc> wrote:
>> >> >>
>> >> >> Am 2021-04-28 13:07, schrieb Andy Shevchenko:
>> >> >> > On Wed, Apr 28, 2021 at 1:51 AM Michael Walle <michael@...le.cc> wrote:
>> >> >> >> Am 2021-04-26 12:29, schrieb Andy Shevchenko:
>> >> >> >> > On Mon, Apr 26, 2021 at 12:55 PM Thomas Bogendoerfer
>> >> >> >> > <tsbogend@...ha.franken.de> wrote:
>> >> >> >> >
>> >> >> >> > 2) there is gpio-regmap generic code, that may be worth
>> >> >> >> > considering.
>> >> >> >>
>> >> >> >> This driver uses memory mapped registers. While that is
>> >> >> >> also possible with gpio-regmap, there is one drawback:
>> >> >> >> it assumes gpiochip->can_sleep = true for now, see [1].
>> >> >> >> Unfortunately, there is no easy way to ask the regmap
>> >> >> >> if its mmio/fastio.
>> >> >> >
>> >> >> > I don't see how it is an impediment.
>> >> >>
>> >> >> You'd have to use the *_cansleep() variants with the gpios,
>> >> >> which cannot be used everywhere, no?
>> >> >
>> >> > *can* sleep means that it requires a sleeping context to run, if your
>> >> > controller is fine with that, there are no worries. OTOH if you want
>> >> > to run this in an atomic context, then consumers can't do with that
>> >> > kind of controller.
>> >>
>> >> Ok, then we are on the same track.
>> >>
>> >> > What I meant above (and you stripped it here) is
>> >> > to add a patch that will fix that and set it based on
>> >> > gpio_regmap_config.
>> >>
>> >> Yes, but ideally, it would ask the regmap. Otherwise that
>> >> information is redundant and might mismatch, i.e. gpio_regmap_config
>> >> tell can_sleep=false but the regmap is an I2C type for example. Also
>> >> if a driver wants to support both regmap types, we are no step
>> >> further.
>> >
>> > Yeah, I agree that is a band aid, but you are free to fix it actually
>> > on regmap level.
>> > I don't think it will require an enormous amount of work there.
>> 
>> I'd love to fix that, but Mark was against exposing that property
>> outside of regmap. So it it what it is for now ;) Maybe he'll change
>> his mind or someone has another idea.
> 
> Then let's go to ugly variant with duplicating it in gpio-regmap
> config. with a FIXME note or so. I don't think we should allow new
> drivers be based on bgpio_init().

Agreed, given that a possible fix should be easy enough later.

-michael