OF device mappings

[Grant Likely]

On Sat, Feb 28, 2009 at 12:18 PM, Gary Thomas <gary at mlbassoc.com> wrote:
> Grant Likely wrote:
>>> How do I find the platform_device which was created when this
>>> particular of_device was instantiated?  I made sure that this code
>>> is run late - after all the of_devices have been handled.
>>
>> Again, there is no platform_device.  of_device *is* the device that was created.
>
> But this doesn't work :-(  I also don't understand how you
> can say "there is no platform_device" - they are everywhere,
> corresponding to actual device instances, as the system
> creates them, typically in a driver 'probe' function.

No, "struct device" is everywhere.  "struct platform_device" is a
particular container for a "struct device", just like "struct
of_device" is another kind of container for "struct device".  The
board setup code (stuff in arch/powerpc/platforms/*) often calls into
the of_platform bus to automatically register an of_device for many of
the nodes in the device tree.  platform_devices are typically
explicitly registered by board setup code and has not relationship
whatsoever with the of_platform bus.

> I've tried both ways.  If I look up the of_platform node and
> then pass the 'dev' structure to the DSA driver, it doesn't work.
> If I look up the actual device instance from the platform_bus
> and pass that to the driver, it does.
>
> How do I get to the proper 'dev' structure which will make the
> DSA driver work?
>
> More details - the DSA driver is expecting to get the 'dev'
> structure pointer which was created in the gianfar driver,
>  static int gfar_probe(struct platform_device *pdev)
> namely '&pdev->dev' -- this works.

Ah, it becomes clear now.  I seen that the gianfar driver has only
recently been converted from a platform bus driver to an of_platform
bus driver (see git commit b31a1d8b41513b96e9c7ec2f68c5734cef0b26a4).
It will be released as part of 2.6.29.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b31a1d8b41513b96e9c7ec2f68c5734cef0b26a4

So, for the kernel version you're using, the
of_find_device_by_phandle() call will never work.  It will for 2.6.29
and beyond.  Currently, there is code in arch/powerpc/sysdev/fsl_soc.c
which creates the platform_device which you're looking for.  Look into
that code to figure out how to get a pointer to that platform_device.
you can probably iterate over the platform bus (hint: look at
bus_find_device() and friends) to find it.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.