On Mon, Feb 02, 2015 at 01:50:52PM +0000, Graeme Gregory wrote:

On Mon, Feb 02, 2015 at 01:40:33PM +0000, Leif Lindholm wrote:

quoted

On Mon, Feb 02, 2015 at 08:45:36PM +0800, Hanjun Guo wrote:

quoted

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 even
if no "acpi=force" is passed in early parameters.

CC: Mark Rutland <mark.rutland@arm.com>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <redacted>
CC: Leif Lindholm <redacted>
CC: Grant Likely <redacted>
CC: Matt Fleming <redacted>
Signed-off-by: Hanjun Guo <redacted>
---
 Documentation/arm/uefi.txt         |  3 +++
 arch/arm64/include/asm/acpi.h      |  1 +
 arch/arm64/kernel/setup.c          | 30 ++++++++++++++++++++++++++++++
 drivers/firmware/efi/libstub/fdt.c |  8 ++++++++
 4 files changed, 42 insertions(+)

diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt
index d60030a..5f86eae 100644
--- a/Documentation/arm/uefi.txt
+++ b/Documentation/arm/uefi.txt

@@ -60,5 +60,8 @@ linux,uefi-mmap-desc-ver  | 32-bit | Version of the mmap descriptor format.
 --------------------------------------------------------------------------------
 linux,uefi-stub-kern-ver  | string | Copy of linux_banner from build.
 --------------------------------------------------------------------------------
+linux,uefi-stub-generated-dtb  | bool | Indication for no DTB provided by
+			       |      | firmware.
+--------------------------------------------------------------------------------

Apologies for the late bikeshedding, but the discussion on this topic
previsously was lively enough that I thought I'd let it die down a bit
before seeing if I had anything to add.

That, and I just realised something:
One alternative to this added DT entry is that we could treat the
absence of a registered UEFI configuration table as the indication
that no HW description was provided from firmware, since the stub does
not call InstallConfigurationTable() on the DT it generates. This does
move the ability to detect to after efi_init(), but this should be
fine for ACPI-purposes.

That would not work as expected in the kexec/Xen use case though as they
may genuinely boot with DT from an ACPI host without UEFI.

I'm a little concerned by this case. How do we intend to pass stuff from
Xen to the kernel in this case? When we initially discussed the stub
prior to merging, we weren't quite sure if ACPI without UEFI was
entirely safe.

The linux,uefi-stub-kern-ver property was originally intended as a
sanity-check feature to ensure nothing (including Xen) masqueraded as
the stub, but for some reason the actual sanity check was never
implemented.

quoted

If that is deemed undesirable, I would still prefer Catalin's
suggested name ("linux,bare-dtb"), which describes the state rather
than the route we took to get there.

I agree.

I guess this would be ok, though it would be nice to know which agent
generated the DTB.

Thanks,
Mark.