From: Grygorii Strashko <grygorii_stras...@epam.com>
Proposal description to add separate SCMI DT node for Xen management agent
under "chosen" or xen-config node, like Hyperlaunch "xen,config".
This proposal introduces a new approach to the Xen multi-domain
configuration, where all Xen-specific configuration has been moved
under the "/chosen" node. This requires less Dom0 device tree
manipulation and isolates Xen configuration from domain configuration.
This approach provides the following device tree (DT) parameters:
- "xen,scmi-secondary-agents": A Xen-specific parameter under the
"/chosen" node, which describes the SCMI agent configuration for
the domains.
- the SCMI configuration for Xen (privileged agent) and the shared
memory configuration for all agents are provided under the "/chosen"
node and are used strictly by Xen for its initial configuration.
- the scmi_shm and SCMI configuration for Dom0 are placed in the
"/firmware/scmi" node so that they can be moved to Dom0 without
any changes.
This configuration allows the use of Xen-specific nodes to provide
information strictly needed by Xen while using the default SCMI
configuration for Dom0 and other domains. As a result, no additional
bindings need to be introduced to the device tree.
Signed-off-by: Grygorii Strashko <grygorii_stras...@epam.com>
Signed-off-by: Oleksii Moisieiev <oleksii_moisie...@epam.com>
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+
+Proposal for SCMI multi-agent driver bindings
+=============================================
+
+Now the Xen configuration for SCMI multi-agent support is done in a bit
complicated way, especially
+from SCMI multi-agent driver initialization and Dom0 DT manipulation point of
view.
+Also it does not take into account future requirements to support SCP SCMI FW.
+
+To enable SCMI multi-agent user need:
+
+* take host DT with basic SCMI enabled
+* add SCMI shared-memory nodes for all agents
+* update SCMI node to point on SCMI Xen management channel (``[smc-id,
shmem]``)
+* add "xen,scmi-secondary-agents" property to the "\chosen" node
+
+.. code::
+
+ chosen {
+ xen,scmi-secondary-agents = <
+ 1 0x82000003 &scmi_shm_1
+ 2 0x82000004 &scmi_shm_2
+ 3 0x82000005 &scmi_shm_3
+ 4 0x82000006 &scmi_shm_4>;
+ }
+
+ /{
+ // SCMI shared-memory nodes for all agents
+ scmi_shm_0 : sram@47ff0000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff0000 0x0 0x1000>;
+ };
+ scmi_shm_1: sram@47ff1000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff1000 0x0 0x1000>;
+ };
+ scmi_shm_2: sram@47ff2000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff2000 0x0 0x1000>;
+ };
+ scmi_shm_3: sram@47ff3000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff3000 0x0 0x1000>;
+ };
+ scmi_shm_4: sram@47ff4000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff4000 0x0 0x1000>;
+ };
+
+ firmware {
+ scmi: scmi {
+ compatible = "arm,scmi-smc";
+ arm, smc - id = <0x82000002>; <--- Xen management agent
channel "smc-id"
+ #address-cells = < 1>;
+ #size-cells = < 0>;
+ #access-controller-cells = < 1>;
+ shmem = <&scmi_shm_0>; <--- Xen management agent channel
"shmem"
+
+ protocol@X{
+ };
+ };
+ };
+ }
+
+Important thing to note is that all information about multi-channel support is
strictly Xen specific.
+
+During initialization the SCMI multi-agent driver uses Host DT SCMI node and
+"xen,scmi-secondary-agents" property to init itself and then, during Dom0
creation, manipulates
+Dom0 DT to remove Xen specific SCMI info and update dom0 SCMI nodes with Dom0
SCMI agent specific
+information.
+
+There are two negative points:
+
+1) Double DT modification - one is user to set up SCMI Xen support in Host DT,
second -
+ Dom0 DT manipulation.
+2) In case of future support of mailbox shared-memory transport there could be
up to 4 mailboxes and
+ up to 2 shared-memories per SCMI agent channel.
+
+Hence SCMI multi-agent support is Xen specific knowledge there is a proposal
to add it as Xen
+specific DT definitions and so minimize Host and Dom0 DT manipulations.
+Those definitions can be added in "/chosen" or, ideally, in "xen,config" node
(like in Hyperlaunch design).
+
+The SCMI binding stays generic, just two SCMI nodes defined - one for Xen
management channel and
+one for Host Dom0 OSPM.
+
+Example of using "chosen" for configuration:
+
+.. code::
+
+ /{
+
+ chosen {
+ ...
+
+ // Xen SCMI management channel
+ scmi_shm_0 : sram@47ff0000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff0000 0x0 0x1000>;
+ };
+ scmi_xen: scmi {
+ compatible = "arm,scmi-smc";
+ arm,smc-id = <0x82000002>; <--- Xen manegement agent smc-id
+ #address-cells = < 1>;
+ #size-cells = < 0>;
+ #access-controller-cells = < 1>;
+ shmem = <&scmi_shm_0>; <--- Xen manegement agent shmem
+ };
+
+ // SCMI multi-agent configuration
+ scmi_shm_2: sram@47ff2000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff2000 0x0 0x1000>;
+ };
+ scmi_shm_3: sram@47ff3000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff3000 0x0 0x1000>;
+ };
+ scmi_shm_4: sram@47ff4000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff4000 0x0 0x1000>;
+ };
+ xen,scmi-secondary-agents = <
+ 1 0x82000003 &scmi_shm
+ 2 0x82000004 &scmi_shm_2
+ 3 0x82000005 &scmi_shm_3
+ 4 0x82000006 &scmi_shm_4>;
+ };
+
+ // Host SCMI OSPM channel - provided to the Dom0 as is if SCMI enabled
for it
+ scmi_shm: sram@47ff1000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff1000 0x0 0x1000>;
+ };
+
+ firmware {
+ scmi: scmi {
+ compatible = "arm,scmi-smc";
+ arm,smc-id = <0x82000003>; <--- Host OSPM agent smc-id
+ #address-cells = < 1>;
+ #size-cells = < 0>;
+ shmem = <&scmi_shm>; <--- Host OSPM agent shmem
+
+ protocol@X{
+ };
+ };
+ };
+ }
+
+
+In the above case:
+
+1) Xen SCMI multi-agent can be probed with DT configuration from "chosen" (or
special "xen,config")
+ node and all Xen related nodes can be easily dropped from Dom0 DT.
+2) Host SCMI OSPM channel DT nodes can be copied to Dom0 DT without changes if
SCMI enabled for it.
+3) Future support for mailbox shared-memory transport (SCP SCMI FW) can be
simplified as no more
+ manipulation required with Dom0 SCMI "arm,smc-id" and "shmem" DT properties.
+
+
+Example of using "xen,config" for configuration:
+
+.. code::
+
+ hypervisor {
+ compatible = “hypervisor,xen”
+
+ // Configuration container
+ config {
+ compatible = "xen,config";
+ ...
+
+ // Xen SCMI management channel
+ scmi_shm_0 : sram@47ff0000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff0000 0x0 0x1000>;
+ };
+ scmi_xen: scmi {
+ compatible = "arm,scmi-smc";
+ arm,smc-id = <0x82000002>; <--- Xen manegement agent smc-id
+ #address-cells = < 1>;
+ #size-cells = < 0>;
+ #access-controller-cells = < 1>;
+ shmem = <&scmi_shm_0>; <--- Xen manegement agent shmem
+ };
+
+ // SCMI multi-agent configuration
+ scmi_shm_2: sram@47ff2000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff2000 0x0 0x1000>;
+ };
+ scmi_shm_3: sram@47ff3000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff3000 0x0 0x1000>;
+ };
+ scmi_shm_4: sram@47ff4000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff4000 0x0 0x1000>;
+ };
+ xen,scmi-secondary-agents = <
+ 1 0x82000003 &scmi_shm
+ 2 0x82000004 &scmi_shm_2
+ 3 0x82000005 &scmi_shm_3
+ 4 0x82000006 &scmi_shm_4>;
+ };
+ };
+
+ /{
+ // Host SCMI OSPM channel - provided to the Dom0 as is if SCMI enabled
for it
+ scmi_shm: sram@47ff1000 {
+ compatible = "arm,scmi-shmem";
+ reg = <0x0 0x47ff1000 0x0 0x1000>;
+ };
+
+ firmware {
+ scmi: scmi {
+ compatible = "arm,scmi-smc";
+ arm,smc-id = <0x82000003>; <--- Host OSPM agent smc-id
+ #address-cells = < 1>;
+ #size-cells = < 0>;
+ shmem = <&scmi_shm>; <--- Host OSPM agent shmem
+
+ protocol@X{
+ };
+ };
+ };
+ }
--
2.34.1
