On 2015?01?20? 02:01, Mark Rutland wrote:

quoted

On Mon, Jan 19, 2015 at 05:52:33PM +0000, Catalin Marinas wrote:

quoted

On Mon, Jan 19, 2015 at 04:59:47PM +0000, Jon Masters wrote:

quoted

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

quoted

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.

Ard had a point, so we should probably not pass acpi=force from EFI stub
(especially since a user may explicitly pass acpi=off irrespective of DT
presence). Some other property in the chosen node? It's not even an ABI
since that's a contract between EFI stub and the rest of the kernel, so
an in-kernel only interface.

Not strictly true once kexec is in place. Then it becomes a stub ->
kernel -> kernel -> kernel -> ... interface, alnog with the rest of the
properties the stub puts in the DTB.

Having something like /chosen/linux,uefi-stub-generated-dtb sounds sane
regardless.

How about the patch (just RFC, maybe it is horrible :) ) below:

When system supporting both DT and ACPI but firmware providing
no dtb, we can use this linux,uefi-stub-generated-dtb property
to let kernel know that we can try ACPI configuration data.

Signed-off-by: Hanjun Guo <redacted>
---
 Documentation/devicetree/bindings/chosen.txt | 19 ++++++++++++++++
 arch/arm64/kernel/setup.c                    | 34
+++++++++++++++++++++++++++-
 drivers/firmware/efi/libstub/fdt.c           |  6 +++++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/chosen.txt

b/Documentation/devicetree/bindings/chosen.txt
index ed838f4..18776b9 100644

--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt

@@ -44,3 +44,22 @@ Implementation note: Linux will look for the property

"linux,stdout-path" or
 on PowerPC "stdout" if "stdout-path" is not found.  However, the
 "linux,stdout-path" and "stdout" properties are deprecated. New platforms
 should only use the "stdout-path" property.
+
+
+linux,uefi-stub-generated-dtb property
+--------------------------------------
+
+UEFI stub will generate this property in the chosen node to let linux kernel
+know that there is no DTB provided by firmware.
+
+There is a use case for system supporting both DT and ACPI, when firmware
+doesn't provide DT, we can try ACPI configration data to boot the system.
+
+Usage:
+
+linux,uefi-stub-generated-dtb = "true" means that it is true that the dtb
+is generated by uefi stub
+
+or
+
+linux,uefi-stub-generated-dtb = "false" is the reverse.