On 01/19/2015 10:13 AM, Grant Likely wrote:

On Mon, 19 Jan 2015 13:51:45 +0000
, Catalin Marinas [off-list ref]
 wrote:

quoted

On Mon, Jan 19, 2015 at 11:55:32AM +0000, Ard Biesheuvel wrote:

quoted

On 19 January 2015 at 11:42, Catalin Marinas [off-list ref] wrote:

quoted

On Wed, Jan 14, 2015 at 03:04:52PM +0000, Hanjun Guo wrote:

quoted

From: Al Stone <redacted>

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.

[...]

quoted

--- 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.

I get the point behind doing this, but could we not have it pass in a
different parameter than =force? Perhaps something new? I'd like to
separate out the case that it was enabled automatically vs explicitly
forced on by a user wanting to use ACPI on a system with both tables.

Jon.