linux-kernel - Re: [PATCH 2/4] ARM: shmobile: r8a7790: add I2C support in Device Tree mode

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Date:	Thu, 26 Sep 2013 02:32:53 -0700
From:	Magnus Damm <magnus.damm@...il.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	SH-Linux <linux-sh@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 2/4] ARM: shmobile: r8a7790: add I2C support in Device
 Tree mode

Hi Guennadi,

On Thu, Sep 26, 2013 at 12:07 AM, Guennadi Liakhovetski
<g.liakhovetski@....de> wrote:
> Hi Magnus
>
> On Thu, 26 Sep 2013, Magnus Damm wrote:
>
>> Hi Guennadi,
>>
>> On Thu, Sep 26, 2013 at 7:10 AM, Guennadi Liakhovetski
>> <g.liakhovetski@....de> wrote:
>> > Hi Laurent
>> >
>> > On Wed, 25 Sep 2013, Laurent Pinchart wrote:
>> >
>> >> Hi Guennadi,
>> >>
>> >> Thank you for the patch.
>> >>
>> >> On Monday 09 September 2013 18:03:54 Guennadi Liakhovetski wrote:
>> >> > This patch adds clocks and clock lookup entries for the four I2C
>> >> > controllers on r8a7790 and respective Device Tree nodes.
>> >> >
>> >> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@...il.com>
>> >> > ---
>> >> >  arch/arm/boot/dts/r8a7790.dtsi         |   36 +++++++++++++++++++++++++++++
>> >> >  arch/arm/mach-shmobile/clock-r8a7790.c |   10 ++++++++
>> >> >  2 files changed, 46 insertions(+), 0 deletions(-)
>> >> >
>> >> > diff --git a/arch/arm/boot/dts/r8a7790.dtsi b/arch/arm/boot/dts/r8a7790.dtsi
>> >> > index 885f9f4..a5021112 100644
>> >> > --- a/arch/arm/boot/dts/r8a7790.dtsi
>> >> > +++ b/arch/arm/boot/dts/r8a7790.dtsi
>> >> > @@ -127,6 +127,42 @@
>> >> >             interrupts = <0 0 4>, <0 1 4>, <0 2 4>, <0 3 4>;
>> >> >     };
>> >> >
>> >> > +   i2c0: i2c@...08000 {
>> >> > +           #address-cells = <1>;
>> >> > +           #size-cells = <0>;
>> >> > +           compatible = "renesas,i2c-rcar-h2";
>> >> > +           reg = <0 0xe6508000 0 0x40>;
>> >> > +           interrupt-parent = <&gic>;
>> >> > +           interrupts = <0 287 0x4>;
>> >>
>> >> Shouldn't you add state = "disabled" to all I2C controllers in order not to
>> >> enable the unused controllers by default ?
>> >
>> > It would be logical, yes, and I seem to remember having discussed this
>> > earlier with someone (with Magnus, IIRC), and the outcome was, that all
>> > Renesas .dtsi files so far define all I2C directly in enabled mode and
>> > that it's intentional, so, I just followed this pattern here. You can
>> > indeed check in other .dtsi files - all seem to do exactly the same.
>>
>> Uhm, I think you mix up platform device use case and DT use case.
>
> I'm sure I don't.

Ok, but it sure sounds like that.

>> In
>> the platform device case we define all devices by default, but that's
>> not how it should be for the DT case. In the case of DT then default
>> should most likely be "disabled". Please follow the direction of
>> Laurent.
>
> To put the record straight - originally I suggested to use status
> "disabled" for mmc devices in .dtsi, before that the status property
> wasn't used in Renesas .dts(i) files, and that's when all I2C nodes were
> already present in .dtsi in enabled state.

Regarding "disabled", using that in a coherent way probably makes
sense. As for MMC, despite my efforts the DT binding development
turned out far from perfect. So during that time the good ideas
proposed may have accidentally been shot down together with the rest,
my apologies for that.

Now, would it be possible to make sure that all mach-shmobile I2C
descriptions follow the same style? I would like the SoCs to be
supported in the same way, not randomly - both then it comes to
compatbile string format and if "disabled" is used or not.

>> Also, I mentioned this 25 times before already so once more cannot
>> hurt: "renesas,i2c-rcar-h2" needs to be replaced with something more
>> standard.
>
> I didn't count, but yes, it has been discussed and that's been fixed in v2
> of my i2c patches. Now that I've got comments to the ARM patches I can
> also update them with a correct compatibility string.

Good, thanks.

/ magnus
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