Unable to boot mainline on snow chromebook since 3.15

[Doug Anderson]

Grant,

On Mon, Sep 8, 2014 at 5:20 AM, Grant Likely <grant.likely at secretlab.ca> wrote:
> On Mon, Sep 8, 2014 at 12:21 PM, Will Deacon <will.deacon at arm.com> wrote:
>> On Sun, Sep 07, 2014 at 05:19:03PM +0100, Tomasz Figa wrote:
>>> At least for next 3.17-rc I'd suggest fixing this up in respective clock
>>> driver and dropping the hack only after Exynos DRM patches are merged
>>> and confirmed working.
>>
>> Whilst I'm sympathetic to people working to enable DRM, I think this is
>> the right solution to the problem. The transition from simplefb to DRM
>> shouldn't break display for a bunch of kernel revisions whilst the code is
>> in flux.
>
> I would go further. The kernel behaviour has changed, and we have to
> deal with platforms that assume the old behaviour. That means either
> defaulting to leaving enabled regulators/clocks alone unless there is
> a flag in the DT saying they can be power managed, or black listing
> platforms that are known to depend on the regulator being on.
>
> Updating the device tree must not be required to get the kernel to
> boot, but it is valid to require a DT upgrade to get better
> performance (battery life) out of the platform.

In this case people using SImple FB are not really using an officially
sanctioned device tree.  The simple-fb fragment is created on the fly
via a "DO NOT SUBMIT" patch sitting on a code review server.  It's not
something that's shipped with real firmware nor is it something
present in the kernel.  See
<https://chromium-review.googlesource.com/#/c/49358/2/board/samsung/smdk5250/smdk5250.c>
as I mentioned above.

Is this really a device tree that we need to guarantee backward
compatibility with?


-Doug