From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
To: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
Cc: Linus Walleij
<linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
Alexandre Courbot
<gnurou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Heikki Krogerus
<heikki.krogerus-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
netdev <netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-wireless"
<linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-sunxi"
<linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org>,
"linux-kernel"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Maxime Ripard
<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>,
"Chen-Yu Tsai" <wens-jdAy2FN1RRM@public.gmane.org>,
Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>,
Mika Westerberg
<mika.westerberg-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
Subject: Re: [PATCH RFC 4/6] net: rfkill: gpio: add device tree support
Date: Tue, 21 Jan 2014 13:35:16 +0100 [thread overview]
Message-ID: <201401211335.16885.arnd@arndb.de> (raw)
In-Reply-To: <CACRpkdYiy+sya6NqRfAmsrFOXvaa3qX=qjRuTDW1vZVSaG1+Gg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Tuesday 21 January 2014, Linus Walleij wrote:
> On Tue, Jan 21, 2014 at 4:11 AM, Alexandre Courbot <gnurou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > On Sat, Jan 18, 2014 at 8:11 AM, Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> >
> > I agree that's how it should be be done with the current API if your
> > driver can obtain GPIOs from both ACPI and DT. This is a potential
> > issue, as drivers are not supposed to make assumptions about who is
> > going to be their GPIO provider. Let's say you started a driver with
> > only DT in mind, and used gpio_get(dev, con_id) to get your GPIOs. DT
> > bindings are thus of the form "con_id-gpio = <phandle>", and set in
> > stone. Then later, someone wants to use your driver with ACPI. How do
> > you handle that gracefully?
>
> Short answer is you can't. You have to pour backward-compatibility
> code into the driver first checking for that property and then falling
> back to the new binding if it doesn't exist.
With the ACPI named properties extension, it should be possible to have
something akin to a "gpio-names" list that can be attached to an indexed
array of gpio descriptors. I assume that Intel is going to need this
for named irqs, clocks, regulators, dmas as well, so I think it will
eventually get there. It's not something that can be done today though,
or that is standardized in APCI-5.0.
My guess is that named GPIOs are going to make more sense on x86 embedded
than on arm64 server.
> > I'm starting to wonder, now that ACPI is a first-class GPIO provider,
> > whether we should not start to encourage the deprecation of the
> > "con_id-gpio = <phandle>" binding form in DT and only use a single
> > indexed GPIO property per device.
>
> You have a valid point.
Independent of ACPI, I prefer indexed "gpios" properties over "con_id-gpio"
properties anyway, because it's more consistent with some of the other
subsystems. I don't have an opinion though on whether we should also
allow a "gpios"/"gpio-names" pair, or whether we should keep the indexed
"gpios" list for the anonymous case.
> > The con_id parameter would then only
> > be used as a label, which would also have the nice side-effect that
> > all GPIOs used for a given function will be reported under the same
> > name no matter what the GPIO provider is.
>
> As discussed earlier in this thread I'm not sure the con_id is
> suitable for labelling GPIOs. It'd be better to have a proper name
> specified in DT/ACPI instead.
+1
> > From an aesthetic point of view, I definitely prefer using con_id to
> > identify GPIOs instead of indexes, but I don't see how we can make it
> > play nice with ACPI. Thoughts?
>
> Let's ask the DT maintainers...
>
> I'm a bit sceptic to the whole ACPI-DT-API-should-be-unified
> just-one-function-call business, as this was just a very simple example
> of what can happen to something as simple as
> devm_gpiod_get[_index]().
I think a unified kernel API makes more sense for some subsystems than
others, and it depends a bit on the rate of adoption of APCI for drivers
that already have a DT binding (or vice versa, if that happens).
GPIO might actually be in the first category since it's commonly used
for off-chip components that will get shared across ARM and x86 (as
well as everything else), while a common kernel API would be less
important for things that are internal to an SoC where Intel is the
only company needing ACPI support.
Arnd
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next prev parent reply other threads:[~2014-01-21 12:35 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-17 6:47 [PATCH RFC 0/6] net: rfkill: gpio: Add device tree support Chen-Yu Tsai
[not found] ` <1389941251-32692-1-git-send-email-wens-jdAy2FN1RRM@public.gmane.org>
2014-01-17 6:47 ` [PATCH RFC 1/6] net: rfkill: gpio: fix gpio name buffer size off by 1 Chen-Yu Tsai
2014-01-17 9:46 ` David Laight
[not found] ` <063D6719AE5E284EB5DD2968C1650D6D45EA9D-VkEWCZq2GCInGFn1LkZF6NBPR1lH4CV8@public.gmane.org>
2014-01-17 9:59 ` Chen-Yu Tsai
2014-01-17 6:47 ` [PATCH RFC 2/6] net: rfkill: gpio: use clk_prepare_enable/clk_disable_unprepare Chen-Yu Tsai
2014-01-17 6:47 ` [PATCH RFC 3/6] net: rfkill: gpio: fix reversed clock enable state Chen-Yu Tsai
2014-01-17 6:47 ` [PATCH RFC 4/6] net: rfkill: gpio: add device tree support Chen-Yu Tsai
[not found] ` <1389941251-32692-5-git-send-email-wens-jdAy2FN1RRM@public.gmane.org>
2014-01-17 16:47 ` Arnd Bergmann
[not found] ` <201401171747.46332.arnd-r2nGTMty4D4@public.gmane.org>
2014-01-17 17:43 ` Chen-Yu Tsai
[not found] ` <CAGb2v67UKiyfJbKZ_Frk3OwZupMPoA2Ck3Hj2zsRFXBQPztavg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-17 20:13 ` Arnd Bergmann
2014-01-17 23:11 ` Linus Walleij
[not found] ` <CACRpkdZOD4zeA8T5kbJ4c5NsnuzHCg1mw8rRMYNT9c4R-Qnc6A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-18 4:41 ` Chen-Yu Tsai
2014-01-20 8:10 ` Heikki Krogerus
2014-01-21 3:11 ` Alexandre Courbot
[not found] ` <CAAVeFuLP4MkfXGG1FMauvUw_J63zRXdhGwxqYy5W98L1wCQNbw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-21 9:35 ` Linus Walleij
[not found] ` <CACRpkdYiy+sya6NqRfAmsrFOXvaa3qX=qjRuTDW1vZVSaG1+Gg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-21 12:35 ` Arnd Bergmann [this message]
[not found] ` <201401211335.16885.arnd-r2nGTMty4D4@public.gmane.org>
2014-01-21 14:53 ` Alexandre Courbot
2014-01-21 15:25 ` Mika Westerberg
[not found] ` <CAAVeFuKFfAvSPYLmvWV5jjT-peZFJ8sJ2bbh4F=JAYoWLhjZpA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-21 18:50 ` Arnd Bergmann
2014-01-22 12:38 ` Mark Brown
2014-01-22 9:54 ` Linus Walleij
2014-01-22 9:58 ` Linus Walleij
[not found] ` <CACRpkdZbb=eO8YRtMn6hW0vn97PkHUo88e_o61DEC8=wPY3_PQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-01-22 11:00 ` Mika Westerberg
2014-01-27 14:24 ` Maxime Ripard
2014-01-29 4:01 ` Chen-Yu Tsai
2014-01-17 6:47 ` [PATCH RFC 5/6] net: rfkill: gpio: add clock-frequency device tree property Chen-Yu Tsai
2014-01-17 6:47 ` [PATCH RFC 6/6] ARM: sun7i: cubietruck: enable bluetooth module Chen-Yu Tsai
2014-01-17 20:26 ` [PATCH RFC 0/6] net: rfkill: gpio: Add device tree support Johannes Berg
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