linux-kernel - Re: [PATCH 3/4] gpio: sifive: Add GPIO driver for SiFive SoCs

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Message-ID: <CACRpkdaDmd+0809wmiNwSRbsdHaDNzpbOaxCcx6bEfYuyzPNQg@mail.gmail.com>
Date:   Fri, 22 Nov 2019 13:28:12 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Yash Shah <yash.shah@...ive.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "Paul Walmsley ( Sifive)" <paul.walmsley@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "maz@...nel.org" <maz@...nel.org>,
        "bmeng.cn@...il.com" <bmeng.cn@...il.com>,
        "atish.patra@....com" <atish.patra@....com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sachin Ghadi <sachin.ghadi@...ive.com>
Subject: Re: [PATCH 3/4] gpio: sifive: Add GPIO driver for SiFive SoCs

On Tue, Nov 19, 2019 at 5:42 PM Bartosz Golaszewski
<bgolaszewski@...libre.com> wrote:
> wt., 19 lis 2019 o 16:03 Linus Walleij <linus.walleij@...aro.org> napisał(a):
> > On Mon, Nov 18, 2019 at 11:15 AM Bartosz Golaszewski
> > <bgolaszewski@...libre.com> wrote:

> > > pon., 18 lis 2019 o 11:03 Yash Shah <yash.shah@...ive.com> napisał(a):
> > Is it really so? The bgpio_lock does protect the registers used
> > by regmap-mmio but unless the interrupt code is also using the
> > same registers it is fine to have a different lock for those.
> >
> > Is the interrupt code really poking into the very same registers
> > as passed to bgpio_init()?
> >
> > Of course it could be seen as a bit dirty to poke around in the
> > same memory space with regmap and the bgpio_* accessors
> > but in practice it's no problem if they never touch the same
> > things.
> >
> > Yours,
> > Linus Walleij
>
> I'm wondering if it won't cause any inconsistencies when for example
> interrupts are being triggered on input lines while we're also reading
> their values? Seems to me it's just more clear to use a single lock
> for a register range. Most drivers using gpio-mmio do just that in
> their irq-related routines.

OK good point. Just one lock for the whole thing is likely
more maintainable even if it works with two different locks.

> Anyway: even without using bgpio_lock this code is inconsistent: if
> we're using regmap for interrupt registers, we should either decide to
> rely on locking provided by regmap or disable it and use a locally
> defined lock.

OK makes sense, let's say we use the bgpio_lock everywhere
for this.

Yash: are you OK with this? (Haven't read the new patch set
yet, maybe it is already fixed...)

> Also: if we're using regmap, then let's use it
> everywhere, not only when it's convenient for updating registers.

I think what you are saying is that we should extend gpio-mmio.c
with some optional regmap API (or create a separate MMIO library
for regmap consumers) which makes sense, but it feels a bit
heavy task to toss at contributors.

We could add it to the TODO file, where I already have some
item like this for port-mapped I/O.

Yours,
Linus Walleij