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

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Date:   Wed, 28 Apr 2021 16:04:32 +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>
Subject: Re: [PATCH v4 1/2] gpio: Add support for IDT 79RC3243x GPIO
 controller

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.

-michael