linux-kernel - Re: [PATCH v6 4/6] gpio: davinci: add OF support

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Date:	Mon, 25 Nov 2013 16:30:09 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Prabhakar Lad <prabhakar.csengg@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Grygorii Strashko <grygorii.strashko@...com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	<linux-gpio@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH v6 4/6] gpio: davinci: add OF support

On Thursday 21 November 2013 11:45 PM, Prabhakar Lad wrote:
> From: KV Sujith <sujithkv@...com>
> 
> This patch adds OF parser support for davinci gpio
> driver and also appropriate documentation in gpio-davinci.txt
> located at Documentation/devicetree/bindings/gpio/.
> 
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> Acked-by: Rob Herring <rob.herring@...xeda.com>
> Signed-off-by: KV Sujith <sujithkv@...com>
> Signed-off-by: Philip Avinash <avinashphilip@...com>
> [prabhakar.csengg@...il.com: simplified the OF code, removed
> 		unnecessary DT property and also simplified
> 		the commit message]
> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
> ---
>  .../devicetree/bindings/gpio/gpio-davinci.txt      |   41 ++++++++++++++
>  drivers/gpio/gpio-davinci.c                        |   57 ++++++++++++++++++--
>  2 files changed, 95 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/gpio/gpio-davinci.txt
> 
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-davinci.txt b/Documentation/devicetree/bindings/gpio/gpio-davinci.txt
> new file mode 100644
> index 0000000..a2e839d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/gpio/gpio-davinci.txt
> @@ -0,0 +1,41 @@
> +Davinci GPIO controller bindings
> +
> +Required Properties:
> +- compatible: should be "ti,dm6441-gpio"
> +
> +- reg: Physical base address of the controller and the size of memory mapped
> +       registers.
> +
> +- gpio-controller : Marks the device node as a gpio controller.
> +
> +- interrupt-parent: phandle of the parent interrupt controller.
> +
> +- interrupts: Array of GPIO interrupt number. Only banked or unbanked IRQs are
> +	      supported at a time.

If this is true..

> +
> +- ti,ngpio: The number of GPIO pins supported.
> +
> +- ti,davinci-gpio-unbanked: The number of GPIOs that have an individual interrupt
> +		             line to processor.

.. then why do you need to maintain this separately? Number of elements
in interrupts property should give you this answer, no?

There can certainly be devices (past and future) which use a mixture of
banked and unbanked IRQs. So a binding which does not take care of this
is likely to change in future and that is a problem since it brings in
backward compatibility of the binding into picture.

The right thing would be to define the DT node per-bank similar to what
is done on OMAP rather than for all banks together. That way there can
be a separate property which determines whether that bank supports
direct-mapped or banked IRQs (or that could be inferred if the number of
tuples in the interrupts property is more than one).

Thanks,
Sekhar

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