[PATCH RFC 1/7] platform: add a device node

[Javier Martinez Canillas]

On Mon, Feb 11, 2013 at 12:24 PM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> On Mon, Feb 11, 2013 at 11:33:19AM +0100, Javier Martinez Canillas wrote:
>> On Mon, Feb 11, 2013 at 9:16 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
>> > On Sun, Feb 10, 2013 at 12:35:43PM +0100, Javier Martinez Canillas wrote:
>> >> On Sun, Feb 10, 2013 at 10:37 AM, Russell King - ARM Linux
>> >> <linux at arm.linux.org.uk> wrote:
>> >> > On Sun, Feb 10, 2013 at 02:49:21AM +0100, Javier Martinez Canillas wrote:
>> >> >> I knew this would be controversial and that's why I didn't mean it to be a patch
>> >> >> but a RFC :)
>> >> >>
>> >> >> The problem basically is that you have to associate the platform device with its
>> >> >> corresponding DT device node because it can be used in the driver probe function.
>> >> >
>> >> > When DT is being used, doesn't DT create the platform devices for you,
>> >> > with the device node already set correctly?
>> >> >
>> >>
>> >> Well they usually do but not always just like usually you have a
>> >> platform_device in your board code and call platform_device_register().
>> >>
>> >> But in some configurations you can't just define the platform_device
>> >> required resources (I/O memory, IRQ, etc) as static platform data.
>> >> In some cases you need a level of indirection.
>> >>
>> >> In this particular case a SMSC ethernet chip is connected to an
>> >> OMAP3 processor through its General-Purpose Memory Controller.
>> >>
>> >> You can't just define the I/O memory used by the device since you first
>> >> need to request that address to the GPMC. The same happens with the
>> >> IRQ line since a OMAP GPIO pin is used so you have to first configure
>> >> the GPIO line as input.
>> >
>> > For the gpio interrupt you can use, example taken from omap4-var-som.dts:
>> >
>> >         interrupt-parent = <&gpio6>;
>> >         interrupts = <11>; /* gpio line 171 */
>> >
>> > Other architectures allow to specify the edge/level hi/low active
>> > parameters from the devicetree aswell. The gpio direction should be
>> > handled by the gpio driver as necessary, at least that's what done on
>> > other architectures.
>> >
>> > If the SMSC hangs on the GPMC then the SMSC should be a child node of
>> > the GPMC. The GPMC would then act as a bus driver and configure the
>> > chipselects and timings for its children automatically, maybe based
>> > on timing information from the devicetree. I've never tried this before,
>> > but I think that's the way things should be.
>> >
>>
>> Hi Sasha,
>>
>> The SMSC is already a child node of the GPMC in the device tree but instead
>> using the generic SMSC binding I added a GPMC-specific SMSC binding.
>>
>> Since the SMSC binding doesn't have a chip select property and it expects
>> the I/O memory address to be explicitly defined in the reg property while
>> the GPMC needs to request this memory according to the chip select used.
>
> So you probably have this:
>
>         gpmc {
>                 compatible = "ti,gpmc", "simple-bus";
>                 ranges;
>
>                 smsc911x {
>                         compatible = "smsc,91x";
>                 }
>         }
>

Yes

> If you remove the simple-bus property the gpmc devices would not be
> probed. If then you add a driver which matches "ti,gpmc" you can
> configure the chip selects in its probe callback. After this you
> can call of_platform_populate() starting from the gpmc device node
> to instantiate the gpmc child devices.
>
> Please somebody interrupt me if I'm talking total rubbish here. I never
> tried this and only assume it should work like this.
>

Nice, I haven't thought about that and I don't see why it shouldn't work.

I won't have time to work on this for at least the next 3 weeks but I'll try
once I have more free time and post another RFC if I got things working.

> Sascha
>

Thanks a lot and best regards,
Javier