On 5/4/20 8:34 PM, Andrei Warkentin wrote:
Hi Grant,
Please also factor in requirements for how memory containing DT must be
described in the memory map (Ard mentioned using EfiACPIReclaimMemory).
Maybe something like:
* Devicetree loaded at boot time must be contained in memory of type
EfiACPIReclaimMemory.
Ack.
Not a strong position, but you may also want to put the foot down on
*when* the exposed Devicetree blob must be consistent (consistent with
some firmware setting changes). Perhaps thats at ReadyToBoot or
ExitBootServices.
ReadyToBoot is a PI concept, not a UEFI concept. And EBS() is way too
late. But I don't think there is any need to specify this: the firmware
needs to make the DT available before calling the OS loader - I don't
think we need to spell that out.
But this brings something else to mind: in the past, we had to push back
on efforts to upstream Linux changes to install the DTB back into the
configuration table, so that at EBS() time, the firmware would see the
modified version. *That* is something we should rule out:
"""
Firmware must not consume device tree descriptions installed as
configuration tables under this GUID by the OS loader or other boot
stages that are not part of the system firmware itself
"""
I don't think the exact choice matters as long as it's
called out, so that an OS loader can be coded to fetch the blob exactly
once at the right time, and be guaranteed to work on any EBBR-compliant
implementation (IIRC ACPI has the same problem, but you have the luxury
of having to worry about that).
You might want to expand the GUID text to be something like:
The following GUID must be used to describe the flattened Devicetree
blob (dtb) in the EFI_CONFIGURATION_TABLE structure referenced by the
EFI System Table.
A
------------------------------------------------------------------------
*From:* Grant Likely <[email protected]>
*Sent:* Monday, May 4, 2020 12:20 PM
*To:* [email protected]
<[email protected]>
*Cc:* Grant Likely <[email protected]>; Andrei Warkentin
<[email protected]>; Francois Ozog <[email protected]>
*Subject:* [EBBR PATCH] Add EFI GUID for device tree blob
None of the relevent specs (EFI, DT, EBBR) specify the GUID for passing
a DTB. Add it to the EBBR document so it is documented somewhere
relevant.
Fixes: #45
Cc: Andrei Warkentin <[email protected]>
Cc: Francois Ozog <[email protected]>
Signed-off-by: Grant Likely <[email protected]>
---
source/chapter2-uefi.rst | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst
index f6a5802..cf2f652 100644
--- a/source/chapter2-uefi.rst
+++ b/source/chapter2-uefi.rst
@@ -86,6 +86,16 @@ tables.
- An Advanced Configuration and Power Interface [ACPI]_ table, or
- a Devicetree [DTSPEC]_ system description
+A Devicetree system description MUST be provided in Flattened
Devicetree (DTB)
+format version 17 or higher.
+The following GUID must be used in the EFT system table to identify the
DTB.
+
+.. code-block:: c
+
+ #define EFI_DTB_GUID \
+ EFI_GUID(0xb1b621d5, 0xf19c, 0x41a5, \
+ 0x83, 0x0b, 0xd9, 0x15, 0x2c, 0x69, 0xaa, 0xe0)
+
As stated above, EBBR systems must not provide both ACPI and Devicetree
tables at the same time.
Systems that support both interfaces must provide a configuration
--
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