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

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Date:   Wed, 28 Apr 2021 17:32:31 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Michael Walle <michael@...le.cc>
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

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.

We have time :-)

-- 
With Best Regards,
Andy Shevchenko