On Tue, Oct 11, 2016 at 02:01:21PM +0100, Mark Rutland wrote:
> On Thu, Oct 06, 2016 at 11:37:04PM +0200, Mark Brown wrote:

> > There's nothing stopping these systems defining a DSD that contains a
> > DTB which overrides some or all of the ACPI if the system supports it
> > (or otherwise providing both system descriptions). 

> Please, no. We very deliberately avoided this mix-and-match scheme for arm64
> (it was proposed in discussions several times), because it suffers form worse
> issues than PRP (since you can't corss-reference between DT and ACPI).

Right, I was mainly thinking of the all case here rather than the some
case.  It's not clear to me that we're not going to end up with the
mixed case anyway as a result of the FPGA work but that's definitely not
my preferred option.

> The arm64 kernel needs a DTB to pass some OS-specific stuff like bootargs, but
> when using ACPI almost everything else is ignored -- we don't unflatten the
> tree and we don't instanciate devices from it.

The important thing here is that that DTB can in fact be a real DT
rather than just the stub and in that case the kernel can pick and
choose (and by default it'll just ignore the ACPI if it can though
some of the distros change that default).