Unable to boot mainline on snow chromebook since 3.15

[Grant Likely]

On Wed, Sep 10, 2014 at 3:31 PM, 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).
>
>> Much better would have been if the DRM changes worked when they
>> landed, so that the migration form simplefb to drm was invisible to
>> the user. Or at least, to get them working ASAP since they're still
>> broken. :(
>
> As far as I can tell the problem here is coming from the decision to
> have simplefb use resources without knowing about them - can we agree
> that this is a bad idea?

No, I don't think we can... there is a certain amount of "firmware got
things working for us, and we're going to use it for a while" that is
absolutely reasonable. simplefb is a good example, but there are
certainly others.

I /do/ think it would be better for the simplefb data to get embedded
or linked into the node of the graphics controller so that it can be
torn down appropriately, and we need a rule for how long boot-state
can be considered valid so that a proper driver can either reserve the
resources for a given SoC, or do a full handoff from the simplefb.
Even without that though, we need to be able to handle the case of an
anonymous simplefb node with no regulator information. If that means
the default simplefb behaviour is to inhibit runtime pm on all
resources until a real driver show up, then that might just be what we
need to do.

Two things should probably be changed from the current setup. 1)
simplefb shouldn't be a platform driver. It is a boot thing that
handles initial state from the graphics chip. By implementing it as a
platform driver, it prevents the real driver from binding to the real
device if the simplefb data embedded into it. 2) make sure that an SoC
driver can protect the needed resources before they are automatically
disabled. Either by putting them in an earlier initcall, or handling
it in the subsystem code. I don't know enough about the regulator and
clock runtime PM to know what the best way to do this is.

g.