linux-kernel - Re: [PATCH] spi: Force the registration of the spidev devices

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Date:	Mon, 5 May 2014 16:22:57 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Mark Brown <broonie@...nel.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] spi: Force the registration of the spidev devices

Hi Alexandre,

On Mon, May 5, 2014 at 3:57 PM, Alexandre Belloni
<alexandre.belloni@...e-electrons.com> wrote:
> On 05/05/2014 at 09:10:43 +0200, Geert Uytterhoeven wrote :
>> On Mon, May 5, 2014 at 6:17 AM, Maxime Ripard
>> <maxime.ripard@...e-electrons.com> wrote:
>> > On Fri, May 02, 2014 at 01:28:26AM +0200, Geert Uytterhoeven wrote:
>> >> On Fri, May 2, 2014 at 12:36 AM, Maxime Ripard
>> >> <maxime.ripard@...e-electrons.com> wrote:
>> >> > But it actually doesn't work in a case where you can't really predict
>> >> > what is on the other side of the bus. Either because, on the board
>> >> > you're using the pins are exposed and it's pretty much up to the user
>> >> > to know what to put on it. That could be handled by DT overlays
>> >> > though.
>> >> >
>> >> > What never works is where the device on the other side is so generic
>> >> > that you really can't tell what it does. Think of a microcontroller
>> >> > that would behave as a SPI slave. It's behaviour and what it does is
>> >> > pretty much dependant of what we flashed on it, and suddenly the
>> >> > compatible string is not the proper reprensentation anymore.
>> >>
>> >> So you will (hopefully soon) use overlay DT to change the DTS to match what's
>> >> connected?
>> >
>> > Not really, because you can't declare a spidev device in the DT.
>>
>> Yes you can. I've done it before.
>>
>> See also "git grep -w spidev -- arch/arm/*/dts/".
>
> I'm pretty sure that doesn't work as there is no compatible matching
> "spidev"

See the last line of spi_match_device():

        return strcmp(spi->modalias, drv->name) == 0;

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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