Hi Ard,
On Wed, Sep 6, 2023, 10:09 Ard Biesheuvel ardb@kernel.org wrote:
On Wed, 6 Sept 2023 at 16:54, Simon Glass sjg@chromium.org wrote:
Hi Rob, Ard,
On Wed, 6 Sept 2023 at 08:34, Rob Herring robh@kernel.org wrote:
On Tue, Sep 5, 2023 at 4:44 PM Ard Biesheuvel ardb@kernel.org wrote:
On Thu, 31 Aug 2023 at 01:18, Simon Glass sjg@chromium.org wrote:
The Devicetree specification skips over handling of a logical view
of
the memory map, pointing users to the UEFI specification.
It is common to split firmware into 'Platform Init', which does the initial hardware setup and a "Payload" which selects the OS to be
booted.
Thus an handover interface is required between these two pieces.
Where UEFI boot-time services are not available, but UEFI firmware
is
present on either side of this interface, information about memory
usage
and attributes must be presented to the "Payload" in some form.
I don't think the UEFI references are needed or helpful here.
This aims to provide an small schema addition for this mapping.
For now, no attempt is made to create an exhaustive binding, so
there are
some example types listed. More can be added later.
The compatible string is not included, since the node name is
enough to
indicate the purpose of a node, as per the existing reserved-memory schema.
Node names reflect the 'class', but not what's specifically in the node. So really, all reserved-memory nodes should have the same name, but that ship already sailed for existing users. 'compatible' is the right thing here. As to what the node name should be, well, we haven't defined that. I think we just used 'memory' on some platforms.
OK
This binding does not include a binding for the memory 'attribute' property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be
useful
to have that as well, but perhaps not as a bit mask.
Signed-off-by: Simon Glass sjg@chromium.org
Changes in v5:
- Drop the memory-map node (should have done that in v4)
- Tidy up schema a bit
Changes in v4:
- Make use of the reserved-memory node instead of creating a new
one
Changes in v3:
- Reword commit message again
- cc a lot more people, from the FFI patch
- Split out the attributes into the /memory nodes
Changes in v2:
- Reword commit message
.../reserved-memory/common-reserved.yaml | 53
+++++++++++++++++++
1 file changed, 53 insertions(+) create mode 100644
dtschema/schemas/reserved-memory/common-reserved.yaml
diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml
b/dtschema/schemas/reserved-memory/common-reserved.yaml
new file mode 100644 index 0000000..d1b466b --- /dev/null +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml @@ -0,0 +1,53 @@ +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause +%YAML 1.2 +--- +$id:
http://devicetree.org/schemas/reserved-memory/common-reserved.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+title: Common memory reservations
+description: |
- Specifies that the reserved memory region can be used for the
purpose
- indicated by its node name.
- Clients may reuse this reserved memory if they understand what
it is for.
+maintainers:
- Simon Glass sjg@chromium.org
+allOf:
- $ref: reserved-memory.yaml
+properties:
- $nodename:
- enum:
- acpi-reclaim- acpi-nvs- boot-code- boot-data- runtime-code- runtime-dataThese types are used by firmware to describe the nature of certain memory regions to the OS. Boot code and data can be discarded, as
well
as ACPI reclaim after its contents have been consumed. Runtime code and data need to be mapped for runtime features to work.
When one firmware phase communicates the purpose of a certain memory reservation to another, it is typically not limited to whether its needs to be preserved and when it needs to be mapped (and with which attributes). I'd expect a memory reservation appearing under this
node
to have a clearly defined purpose, and the subsequent phases need to be able to discover this information.
For example, a communication buffer for secure<->non-secure communication or a page with spin tables used by PSCI. None of the proposed labels are appropriate for this, and I'd much rather have a compatible string or some other property that clarifies the nature in a more suitable way. Note that 'no-map' already exists to indicate that the CPU should not map this memory unless it does so for the specific purpose that the reservation was made for.
I agree. I think compatible is the better approach. Some property like 'discard' may not be sufficient information if the OS needs to consume the region first and then discard it. Better to state exactly what's there and then the OS can imply the rest.
OK, so what sort of compatible strings?
How about: "acpi-reclaim" - holds ACPI tables; memory can be reclaimed once the tables are read and no-longer needed
ACPI reclaim is a policy, not a purpose. This memory could contain many different things.
"boot-code" - holds boot code; memory can be reclaimed once the boot phase is complete "runtime-code" - holds runtime code; memory can be reclaimed only if this code will not be used from that point
These are also policies. They can be inferred from the purpose.
etc. We can then have more specific compatibles, like:
"psci-spin-table" - holds PSCI spin tables
so you could do:
compatible = "runtime-code", "psci-spin-table";
I understand that this binding targets firmware<->firmware rather than firmware<->OS, which makes it much more difficult to keep it both generic and sufficiently descriptive.
However, I still feel that all the overlap with UEFI memory types is not what we want here. UEFI knows how to manage its own memory map, what it needs to know is what memory is already in use and for which exact purpose. Whether or not that implies that the memory can be freed at some point or can be mapped or not should follow from that.
Can you please make a suggestion? I am unsure what you are looking for.
Regards, Simon