On 01/09/2020 11:53, Peter Robinson wrote:
On Tue, Sep 1, 2020 at 11:48 AM Grant Likely <[email protected]> wrote:
Early in EBBR discussions the decision was made that firmware should not
provide both DT and ACPI at the same time. The reasoning had been that
we didn't want to encourage 'hybrid' approaches where the OS tries to
consume both DT and ACPI descriptions.
However, this fear has not so-far born out, and feedback has been that
requiring a boot-time switch to select either DT or ACPI is a support
issue for OS vendors. They would rather see ACPI (or DT) always turned
on if it is an option and the OS can choose to use it or not.
Thoughts? Can the exclusive or be relaxed here?
The problem I have seen here from a OS support perspective is that you
can get different levels of functionality on the OS side of things
depending on which the OS chooses to priortise/support and that then
just moves the support issue elsewhere.
We're always going to have that issue on platforms that have both DT and
ACPI support. Realistically, the target audience of EBBR are embedded
SBCs that use DT+Linux today, but are are now eyeing OSes that only use
ACPI. In all likelyhood, DT will continue to be the preferred system
description for Linux OSes, but the ones that cannot consume DT will
make use of ACPI.
It does shift the problem, but it shifts the problem to a place the OS
vendor has control over (e.g. choosing whether to consume DT or ACPI)
rather than an opaque switch in firmware.
g.
Signed-off-by: Grant Likely <[email protected]>
---
source/chapter2-uefi.rst | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
index 066fefb..e0e71d6 100644
--- a/source/chapter2-uefi.rst
+++ b/source/chapter2-uefi.rst
@@ -80,18 +80,12 @@ Configuration Tables
A UEFI system that complies with this specification may provide the additional
tables via the EFI Configuration Table.
-Compliant systems are required to provide one, but not both, of the following
+Compliant systems are required to provide at least one of the following
tables:
- an Advanced Configuration and Power Interface [ACPI]_ table, or
- a Devicetree [DTSPEC]_ system description
-EBBR systems must not provide both ACPI and Devicetree
-tables at the same time.
-Systems that support both interfaces must provide a configuration
-mechanism to select either ACPI or Devicetree,
-and must ensure only the selected interface is provided to the OS loader.
-
Devicetree
^^^^^^^^^^
--
2.20.1
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