Subject: Re: [PATCH 1/2] dt-bindings: arm: arm,scmi: add smc/hvc transports

On Fri, Feb 07, 2020 at 10:08:36AM +0000, Marc Zyngier wrote:

quoted

On 2020-02-06 13:01, peng.fan@nxp.com wrote:

quoted

From: Peng Fan <peng.fan@nxp.com>

SCMI could use SMC/HVC as tranports, so add into devicetree binding
doc.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 Documentation/devicetree/bindings/arm/arm,scmi.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/arm/arm,scmi.txt

b/Documentation/devicetree/bindings/arm/arm,scmi.txt
index f493d69e6194..03cff8b55a93 100644

--- a/Documentation/devicetree/bindings/arm/arm,scmi.txt
+++ b/Documentation/devicetree/bindings/arm/arm,scmi.txt

@@ -14,7 +14,7 @@ Required properties:

 The scmi node with the following properties shall be under the

/firmware/ node.

-- compatible : shall be "arm,scmi"
+- compatible : shall be "arm,scmi" or "arm,scmi-smc"
 - mboxes: List of phandle and mailbox channel specifiers. It should
contain
 	  exactly one or two mailboxes, one for transmitting messages("tx")
 	  and another optional for receiving the notifications("rx") if @@
-25,6 +25,8 @@ The scmi node with the following properties shall be
under the /firmware/ node.
 	  protocol identifier for a given sub-node.
 - #size-cells : should be '0' as 'reg' property doesn't have any size
 	  associated with it.
+- arm,smc-id : SMC id required when using smc transports
+- arm,hvc-id : HVC id required when using hvc transports

 Optional properties:

Not directly related to DT: Why do we need to distinguish between SMC
and HVC?

IIUC you want just one property to get the function ID ? Does that align with
what you are saying ? I wanted to ask the same question and I see no need for
2 different properties.

The multiple protocols might use SMC or HVC. Saying

 Protocol@x {
    method="smc";
    arm,func-id=<0x....>
 };
 Protocol@y {
    method="hvc";
    arm,func-id=<0x....>
 };

With my propose:

Protocol@x {
    arm,smc-id=<0x....>
 };
 Protocol@y {
    arm,hvc-id=<0x....>
 };

No need an extra method property to indicate it is smc or hvc.
The driver use take arm,smc-id as SMC, arm,hvc-id as HVC.

Thanks,
Peng.

quoted

Other SMC/HVC capable protocols are able to pick the right one based
on the PSCI conduit.

This make it clear, but I am asking to  be sure.

quoted

This is how the Spectre mitigations work already. Why is that any different?

I don't see any need for it to be different.

--
Regards,
Sudeep

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel