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

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Message-ID: <CAMpxmJUq_YLU4ha1hTzDUKYMxD36Yb-6C3SraMHgZywx=bm=eA@mail.gmail.com>
Date:   Fri, 22 Nov 2019 13:39:20 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Linus Walleij <linus.walleij@...aro.org>
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

pt., 22 lis 2019 o 13:28 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> 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.
>

It's been on my personal TODO list too for some time as it seems it
could benefit some i2c drivers too. Also: I think such a helper could
eventually completely replace the generic drivers such as gpio-mmio
and gpio-reg.

In other words: good idea to put it into the TODO. If there are no
objections I was thinking about starting the work soon aiming at v5.6,
as soon as we get the recent changes in uAPI out of the way.

Bart

> Yours,
> Linus Walleij