Re: [PATCH 1/2] mmc: add Device Tree properties for UHS modes

[Pawel Moll <pawel.moll@arm.com>]

On Mon, 2013-07-29 at 13:05 +0100, Guennadi Liakhovetski wrote:
> No, that's exactly the problem. We absolutely do not want to write 
> compatible="vendor,soc-v1"; in a .dts file for SoC v2 just because we 
> currently think, that we don't have to distinguish between those SoC 
> versions in this specific driver. I think we all know it quite well, that 
> there are (practically) always differences - sometimes documented, 
> sometimes undocumented. And if you later find out, that you do have to 
> differentiate in the driver - it's too late. Even if we disregard the 
> argument of ugliness of having to set compatibility with soc-v1, soc-v2, 
> soc-v3 in different DT nodes on an SoC v4.

First of all I think your example calls for more than one compatible
string - if it seems that soc,v2 is almost like soc,v1, make it
compatible = "soc-v2", "soc-v1" and don't touch the driver (as in: keep
it compatible with "soc-v1" only). Then, when the realisation comes, you
can simply add the "soc-v2" of_device_id with .data pointing at new
features.

Now the other thing - do you have a driver for a SoC at all? What I mean
is that in most cases it's the components/peripherals/IPs (whatever you
call them) matter, not the SoC itself, so the SoC compatible value can
be unique if you wish (and, if it is a *.dtsi, it will be compatbile
with "simple-bus" anyway ;-). Then the IP nodes can follow the rule
above.

Hope it makes some sense?

Pawel