Unable to boot mainline on snow chromebook since 3.15

[Olof Johansson]

On Wed, Sep 10, 2014 at 7:31 AM, 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).

Yes, having a stage that fixes up broken device trees makes a lot of
sense. It can likely be plugged into the machine descriptor today per
platform, since I think most things we have going on right now are
platform-specific quirks.

I'm strongly against doing this outside of the kernel, since they're
closely tied together today. We've always had the quirk tables for
devices in the kernel, and we used to do this a long time ago on
powerpc as well (we did it before we built the flat DT out of the OF
equivalent there, most of the time).

>> 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?

As already argued, there are good reasons to sometimes allow this, as
long as it can be expected that it's something that's just used during
early boot. For example, having DEBUG_LL output on a pre-mapped
framebuffer could be really useful. Once DRM comes up, it'll tear down
the existing one.


-Olof