[RFC/PATCH] ARM: mvebu: Don't apply the quirks if the SoC revision is unknown

[Ezequiel Garcia]

Hi Gregory,

On 10 Jun 05:39 PM, Gregory CLEMENT wrote:
> On 10/06/2014 15:40, Ezequiel Garcia wrote:
> > On 10 Jun 10:21 AM, Arnd Bergmann wrote:
> >> On Monday 09 June 2014 16:27:16 Ezequiel Garcia wrote:
> >>> We currently skip the I2C and thermal quirks only if the SoC revision is
> >>> known to be one that does not need them. If the SoC revision cannot be
> >>> obtained, the current behavior is to apply the quirk assuming it's needed.
> >>>
> >>> This commit changes this, by requiring the SoC revision to be known in order
> >>> to peform a quirk.
> >>
> >> This clearly needs a better description if we want to apply it. We had
> >> a rather long discussion when the code was first added exactly this
> >> way and you should explain which of the assumptions we made back then
> >> are now incorrect.
> >>
> >> Is it ever wrong (as opposed to inefficient) to apply the quirk even on a
> >> newer SoC?
> >>
> > 
> > Yes, for the thermal quirk it is wrong as it consists in changing the compatible
> > string and moving the registers around.
> > 
> > So if you apply the quirk on a SoC that doesn't need it, thermal won't work.
> 
> Actually it is the opposite for the I2C quirk. If you don't apply it on an SoC
> which needs it then the i2C won't work, whereas if you apply it on an SoC which
> don't need it, then you won't benefit of an optimization but the I2C will remain
> usable.
> 
> So with your change we can have a situation where the i2c is no more usable.
> That's why I would prefer that you don't modify the i2c quirk.
> 

Thanks a lot for clarifying this point. I'll prepare a v2, changing only the
thermal quirk, and explaining the difference in a comment and in the commit
log.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com