Re: [alsa-devel] [RFC] ucb1400 touchscreen, irq auto probing and ac97 with its private field

[Mark Brown <broonie@opensource.wolfsonmicro.com>]

On Fri, Apr 25, 2008 at 09:02:27AM +0200, Takashi Iwai wrote:
> Mark Brown wrote:

> > I think about it it may be best to just do the same thing as the
> > platform bus does and define accessor macros for getting at this from a
> > struct snd_ac97).

> Not really as same as device_data.  Normally, device data is handled
> by superseding the base device class (just includes struct device) and
> retrieve the class via container_of() or such.

That's normal usage for getting generic class data, not for obtaining
information specific to a particular driver.

> In this case, however, you don't know exactly whether the given struct
> ac97 is really created by the specific controller, and thus you cannot
> assume that the ac97 can be cast to its specific class.

Right, which is why the device_data pointer is used by things like
platform drivers for getting device-specific (as opposed to class
specific) data into the driver from the machine code.

> For multiple anonymous data, we can use a data with a key like below:

This sounds like a reinvention of OpenFirmware, which presents pretty
much the same sort of key/value interface.  It'd be nice to be able to
share the same client code.

> and the controller driver assigns the data like

Doing this would mean that the controller would need to be modified for
each system that wants to pass configuration data to a driver - at that
point much of the win from providing an interface like this is lost.