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

[Grant Likely <grant.likely@linaro.org>]

On Mon, 19 Jan 2015 13:51:45 +0000
, Catalin Marinas <catalin.marinas@arm.com>
 wrote:
> On Mon, Jan 19, 2015 at 11:55:32AM +0000, Ard Biesheuvel wrote:
> > On 19 January 2015 at 11:42, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > On Wed, Jan 14, 2015 at 03:04:52PM +0000, Hanjun Guo wrote:
> > >> From: Al Stone <al.stone@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.

Ditto for me. I think this is a fine solution. And, yes, the stub can
easily detect the presence of ACPI by looking in the UEFI config table.

g.