Re: GPIO - marking individual pins (not) available in device tree

[David Gibson <david@gibson.dropbear.id.au>]

On Sun, Oct 26, 2008 at 04:13:26PM -0500, Matt Sealey wrote:
>
>
> Mitch Bradley wrote:
>>
>> I don't use device_type much, if at all, anymore.  Generic name +  
>> compatible just works better than device_type + specific name.  When
> > I write code that has to find a node that is suitable for a given purpose,
> > I look for the existence of suitable methods and perhaps other properties.
> > I was just too hard to keep the list of device_type values properly
> > synchronized with all the possible things that you might want to infer
> > from that set of names.
>
> The simple problem comes when you define a device_type for everything,
> I do agree it's best not to add any *MORE* that aren't in the IEEE1275
> or CHRP etc. bindings, but for those that still exist and are well
> defined (serial port probably the best, but network devices too) I
> think we should keep using them where possible and where relevant.

device_type in 1275 defines the runtime method interface.  It's *not*
for declaring the general class of the device, although it often
matches that in practice.  Drivers which attempt to use it this way
are buggy.

So, in the  case of a real OF implementation,  yes, you should include
device_type values as specified by 1275.  Assuming of course that your
implementation  really  does  implement  the OF  method  binding  that
matches the stated device_type.  However, flattened trees clearly
can't provide the method interface, and so shouldn't declare the
device_type.

In practice, we do suggest including device_type in certain, limited,
circumstances precisely because there are a whole bunch of buggy
drivers out there which match (at least partly) on device_type.  We
don't want to break these gratuitously, but neither do we want to
encourage any further spread of using device_type incorrectly for
driver matching.  Hence the current policy.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson