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

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

On Mon, 29 Jul 2013, Pawel Moll wrote:

> 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.

Yes, this is also a possibility, but it seems only a little bit better. 
Why should a DT node on SoC vN have a compatible string with SoC vK for 
some random for an abstract user absolutely unrelated SoC version?... And 
that vK would be different for different devices... So on SoC v5 MMC can 
be compatible with with v1, sound with v2, camera with v3... Don't you 
think it would look like a mess?

> 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.

Sure, I don't mean the top-level root compatibility, I mean device 
compatibility.

Thanks
Guennadi

> Hope it makes some sense?
> 
> Pawel

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/