linux-kernel - Re: [RFC 4/4] ARM: shmobile: r8a7790: adapt DTS for I2C slave support

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Message-ID: <CAMuHMdVi+6TXH68ddQ-UWfUif0Mv=ETu6dnpiy1Apike6zfAbg@mail.gmail.com>
Date:	Fri, 12 Sep 2014 12:10:37 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Marc Dietrich <marvin24@....de>,
	Linux I2C <linux-i2c@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Jean Delvare <jdelvare@...e.de>,
	Magnus Damm <magnus.damm@...il.com>,
	Andrey Danin <danindrey@...l.ru>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>
Subject: Re: [RFC 4/4] ARM: shmobile: r8a7790: adapt DTS for I2C slave support

Hi Wolfram,

On Fri, Sep 12, 2014 at 11:58 AM, Wolfram Sang <wsa@...-dreams.de> wrote:
> 2) Slave mode is needed for board bringup
>
> Some other components need a specific I2C slave to be present before
> userspace is available, otherwise the system is unusable. This is IMO
> then a hardware description and justifies DT entries:

OK, I didn't think this case, which is similar to an external device requiring
a GPIO to be at a specific level.

> DT pseudocode:
>
>         i2c {
>                 compatible = "nvidia, tegra-i2c";
>
>                 ec-slave@42 {
>                         compatible = "nvidia, ax100-ec-slave";
>                         reg = <0x42>;
>                 };
>         };

So distinguishing between drivers providing slave services (using slave
mode) and drivers driving actual slave hardware (using master mode) is
done based on the compatible-property.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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