linux-kernel - Re: [PATCH v7] regulator: fixed: Convert to use GPIO descriptor only

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Date:   Thu, 11 Oct 2018 14:15:36 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Alexander Shiyan <shc_work@...l.ru>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Philipp Zabel <philipp.zabel@...il.com>,
        Daniel Mack <zonque@...il.com>,
        Marc Zyngier <marc.zyngier@....com>,
        jacopo <jacopo@...ndi.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH v7] regulator: fixed: Convert to use GPIO descriptor only

On Thu, Oct 11, 2018 at 11:46:59AM +0200, Marek Szyprowski wrote:
> On 2018-10-11 11:29, Linus Walleij wrote:
> > On Thu, Oct 11, 2018 at 11:01 AM Marek Szyprowski

> >> I've just noticed that this patch causes regression on Samsung
> >> Exynos4412-based Trats2 board. Conversion to GPIO descriptor breaks
> >> operation when regulators used shared GPIO:  sii9234 i2c driver
> >> is not able to get vcc33mhl regulator (it uses shared GPIO enable
> >> line with vsil12 regulator).

> > So I guess this means that this physical GPIO line will enable the
> > vcc33mhl and the vsil12 regulators at the same time?

> Right. It is so common case, that regulator core has special code for
> handling shared enable GPIO.

Yes, and we've discussed it several times already.

> > I was aware of the usecase "several consumers takes the same
> > GPIO line" (Mark told me several times...) so it was in the back of
> > my mind, but it's just hard to see when we were gonna run into it.
> > So it is the fixed regulators, on Samsung boards, I see.

> I don't think this is Samsung specific. I saw similar solution on various
> other boards too. Sharing enable gpio is rather common thing. The issue
> happens if there are separate drivers for each hw block and they need to
> enable it from their code.

It's really common, yeah - things like controlling the power for an
entire chip with one GPIO for all the regulators supplying that chip for
example.  I think what you're seeing here is that Samsung are among the
most active testers of -next (thanks!) rather than that their hardware
is particularly weird.

> > So I was thinking to introduce
> > gpiod_get_nonexclusive() to explicitly handle this case for the few
> > systems that use shared GPIO lines, let me see what I can do.

> The old interface also didn't allow sharing GPIO easily, so regulator
> core has special code for shared enable gpio. However I still have no
> idea how to do this cleanly using descriptor.

Yes, it's been discussed several times and I thought Linus had some idea
for it - IIRC it was a gpiod_is_equal() or something.  You can also do
this by converting descriptors back to numbers and comparing the numbers
but obviously the numbers are supposed to be being removed.

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