linux-kernel - Re: [PATCH 2/4] net: rfkill: gpio: remove gpio names

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Message-ID: <20140227200631.GA43312@mtgdev.linux.intel.com>
Date:	Thu, 27 Feb 2014 12:06:31 -0800
From:	mark gross <mgross@...ux.intel.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	"Gross, Mark" <mark.gross@...el.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Chen-Yu Tsai <wens@...e.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Johannes Berg <johannes@...solutions.net>,
	"David S. Miller" <davem@...emloft.net>,
	Rhyland Klein <rklein@...dia.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Westerberg, Mika" <mika.westerberg@...el.com>
Subject: Re: [PATCH 2/4] net: rfkill: gpio: remove gpio names

On Thu, Feb 27, 2014 at 10:47:58AM -0700, Stephen Warren wrote:
> On 02/27/2014 10:38 AM, Gross, Mark wrote:
> > Please know that no one should not consider me an authority on ACPI at this
> > time.  But, I have some comments / context / thoughts below.
> > 
> > Also I apologize in advance for any email formatting issues caused by
> > replying to this via my work exchange account / outlook client.  Folks can
> > use mgross@...ux.intel.com to avoid outlook-isms from me in the future.
> > 
> >> -----Original Message-----
> >> From: Linus Walleij [mailto:linus.walleij@...aro.org]
> >> Sent: Tuesday, February 25, 2014 1:14 AM
> >> To: Stephen Warren; Alexandre Courbot; Grant Likely;
> >> devicetree@...r.kernel.org
> >> Cc: Chen-Yu Tsai; Heikki Krogerus; Johannes Berg; David S. Miller; Rhyland
> >> Klein; linux-wireless; netdev; linux-kernel; Arnd Bergmann; Gross, Mark
> >> Subject: Re: [PATCH 2/4] net: rfkill: gpio: remove gpio names
> >>
> >> On Fri, Feb 21, 2014 at 6:35 AM, Stephen Warren
> >> <swarren@...dotorg.org> wrote:
> >>> On 02/20/2014 06:55 PM, Chen-Yu Tsai wrote:
> >>
> >>>> That's correct. However using con_id to pass this results in
> >>>> different behavior across DT and ACPI. A better way is to export the
> >>>> labeling function so consumers can set meaningful labels themselves.
> >>>
> >>> But this code is the consumer of those GPIOs. IF the parameter to
> >>> devm_gpiod_get_index() isn't intended to be used, why does it exist?
> >>
> >> Kerneldoc says:
> >>
> >> /**
> >>  * gpiod_get_index - obtain a GPIO from a multi-index GPIO function
> >>  * @dev:        GPIO consumer, can be NULL for system-global GPIOs
> >>  * @con_id:     function within the GPIO consumer
> >>  * @idx:        index of the GPIO to obtain in the consumer
> >>  *
> >>
> >> Basically it is just exposing the fact that of_find_gpio() and
> >> acpi_find_gpio() both take a con_id as argument.
> >>
> >> If we drill into this, we find that it is used to conjure the arbitrary string
> >> before the gpios in the DT case, like:
> >>
> >> foo-gpios = <...>;
> >>
> >> As in tegra30-beaver.dts...
> >>
> >>     sdhci@...00000 {
> >>             status = "okay";
> >>             cd-gpios = <&gpio TEGRA_GPIO(I, 5) GPIO_ACTIVE_LOW>;
> >>             wp-gpios = <&gpio TEGRA_GPIO(T, 3) GPIO_ACTIVE_HIGH>;
> >>             power-gpios = <&gpio TEGRA_GPIO(D, 7) GPIO_ACTIVE_HIGH>;
> >>             bus-width = <4>;
> >>     };
> >>
> >> Instead of passing the GPIOs as index 0,1,2 they are named and I do admit
> >> this has a nice "things are under control" aspect to it.
> >
> > [Gross, Mark] FWIW I don't think this is as "under control" as you do.  Those
> > names in the above sdhci example are derived from a specific SDHCI
> tegra spec
> > sheet or schematic.  Those names likely come from the data sheet for
> > the controller.
> 
> The names of the properties are fixed and defined by the DT binding for
> the Tegra SDHCI controller, or even the core SDHCI bindings. Hence, they
> will be the same in every DT file that uses that Tegra SDHCI compatible
> value (the compatible property isn't show above, because the above
> fragment is a board.dts file, and the compatible value gets inherited
> from the soc.dtsi file). There won't be any variation at all,
> irrespective of what signal names exist in a particular board schematic.
> 
> If there were ever an (upstream?) ACPI "binding"(?) for the Tegra SDHCI
> controller, I would hope it would use the exact same names for the GPIO
> signals.

me to!
--mark
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