linux-kernel - Re: [PATCH 3/5] mmc: slot-gpio: use gpiod_set_active

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Date:   Thu, 14 Sep 2023 10:31:48 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Andy Shevchenko <andy@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Harvey Hunt <harveyhuntnexus@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Daniel Scally <djrscally@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mtd@...ts.infradead.org, platform-driver-x86@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 3/5] mmc: slot-gpio: use gpiod_set_active_[low|high]()

On Wed, Sep 13, 2023 at 2:39 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> On Wed, Sep 13, 2023 at 2:24 PM Linus Walleij <linus.walleij@...aro.org> wrote:
> >
> > On Wed, Sep 13, 2023 at 1:50 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > We have new, less cumbersome and clearer interfaces for controlling GPIO
> > > polarity. Use them in the MMC code.
> > >
> > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > I like the looks of the code better, obviously but this looks like this for
> > a reason unfortunately.
> >
> > See the following from
> > Documentation/devicetree/bindings/mmc/mmc-controller.yaml:
> >
> >   # CD and WP lines can be implemented on the hardware in one of two
> >   # ways: as GPIOs, specified in cd-gpios and wp-gpios properties, or
> >   # as dedicated pins. Polarity of dedicated pins can be specified,
> >   # using *-inverted properties. GPIO polarity can also be specified
> >   # using the GPIO_ACTIVE_LOW flag. This creates an ambiguity in the
> >   # latter case. We choose to use the XOR logic for GPIO CD and WP
> >   # lines.  This means, the two properties are "superimposed," for
> >   # example leaving the GPIO_ACTIVE_LOW flag clear and specifying the
> >   # respective *-inverted property property results in a
> >   # double-inversion and actually means the "normal" line polarity is
> >   # in effect.
> >
>
> I hate it, thanks. :)
>
> > Will you still provide the desired "double inversion" after this patch?
> >
>
> Not in the current form. Would it work to go:
>
> if (override_active_level) {
>     if (!(host->caps2 & MMC_CAP2_CD_ACTIVE_HIGH))
>         gpiod_set_active_high(desc);
>     else
>         gpiod_set_active_low(desc);
> } else {
>     if (host->caps2 & MMC_CAP2_CD_ACTIVE_HIGH)
>         gpiod_set_active_high(desc);
>     else
>         gpiod_set_active_low(desc);
> }
>
> ?

I *think* so but my boolean parser i known to be flawed since I have
screwed up double inversions repeatedly over the years, so it should
not be trusted at all.

> Alternatively we could reimplement the toggle semantics locally in a
> helper function in order to get rid of it from GPIOLIB.

I don't know about that, the flag is inside gpio_desc so we cannot
access it (struct is private to gpiolib...)

Yours,
Linus Walleij