[PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi" and pass acpi=force to enable ACPI

[Catalin Marinas]

On Mon, Jan 19, 2015 at 11:55:32AM +0000, Ard Biesheuvel wrote:
> On 19 January 2015 at 11:42, Catalin Marinas <catalin.marinas at arm.com> wrote:
> > On Wed, Jan 14, 2015 at 03:04:52PM +0000, Hanjun Guo wrote:
> >> From: Al Stone <al.stone at linaro.org>
> >>
> >> Introduce one early parameters "off" and "force" for "acpi", acpi=off
> >> will be the default behavior for ARM64, so introduce acpi=force to
> >> enable ACPI on ARM64.
> >>
> >> Disable ACPI before early parameters parsed, and enable it to pass
> >> "acpi=force" if people want use ACPI on ARM64. This ensures DT be
> >> the prefer one if ACPI table and DT both are provided at this moment.
> > [...]
> >> --- a/arch/arm64/kernel/setup.c
> >> +++ b/arch/arm64/kernel/setup.c
> >> @@ -62,6 +62,7 @@
> >>  #include <asm/memblock.h>
> >>  #include <asm/psci.h>
> >>  #include <asm/efi.h>
> >> +#include <asm/acpi.h>
> >>
> >>  unsigned int processor_id;
> >>  EXPORT_SYMBOL(processor_id);
> >> @@ -388,6 +389,8 @@ void __init setup_arch(char **cmdline_p)
> >>       early_fixmap_init();
> >>       early_ioremap_init();
> >>
> >> +     disable_acpi();
> >> +
> >>       parse_early_param();
> >>
> >>       /*
> >
> > Did we get to any conclusion here? DT being the preferred one is fine
> > when both DT and ACPI are present but do we still want the kernel to
> > ignore ACPI altogether if DT is not present? It's a bit harder to detect
> > the presence of DT at this point since the EFI_STUB added one already. I
> > guess we could move the "acpi=force" argument passing to EFI_STUB if no
> > DT is present at boot.
> 
> Since the EFI stub populates the /chosen node in DT, I would prefer
> for it to add a property there to indicate whether it created the DT
> from scratch rather than adding ACPI specific stuff in there (even if
> it is just a string to concatenate)

This works for me. So we could pass "acpi=force" in EFI stub if it
created the DT from scratch *and* ACPI tables are present (can it detect
the latter? And maybe it could print something if none are available).
If that works, the actual kernel can assume that ACPI needs to be
explicitly enabled via acpi=force, irrespective of how much information
it has in DT.

-- 
Catalin