Unable to boot mainline on snow chromebook since 3.15

[Grant Likely]

On Wed, 10 Sep 2014 15:31:44 +0100, Mark Brown <broonie at kernel.org> wrote:
> On Wed, Sep 10, 2014 at 06:06:46AM -0700, Olof Johansson wrote:
> > On Mon, Sep 8, 2014 at 12:40 PM, Grant Likely <grant.likely at secretlab.ca> wrote:
> 
> > > Well, lets see... We've got a real user complaining about a platform
> > > that used to work on mainline, and no longer does. The only loophole
> > > for ignoring breakage is if there nobody cares that it is broken. That
> > > currently isn't the case. So even though it's based on a patch that
> > > has "DO NOT SUBMIT" in large friendly letters on the front cover, it
> > > doesn't change the situation that mainline has a regression.
> 
> > Yeah, I'm with you on this Grant, it doesn't matter what the patch is
> > labelled as.
> 
> > One way to deal with this could be to add a quirk at boot time --
> > looking for the simplefb and if found, modifies the regulators to keep
> > them on. That'd go in the kernel, not in firmware.
> 
> Well, we should also be fixing simplefb to manage the resources it uses
> though that doesn't clean up after the broken DTs that are currently
> deployed.
> 
> As well as the regulators we'll also need to fix the clocks.  If we're
> going to start adding these fixups perhaps we want to consider having a
> wrapper stage that deals with rewriting DTs prior to trying to use them?
> I'm not sure if it makes much difference but there's overlap with other
> tools like the ATAGs conversion wrapper and building separately would
> let the fixup code run early without directly going into the early init
> code (which seems a bit scary).

We've already got a dt fixup hook in the machine struct, created for
exactly this reason. Fixing an incorrect DT provided by firmware:

arch/arm/include/asm/mach/arch.h:
struct machine_desc {
	...
	void (*dt_fixup)(void);
	...

g.