Re: [PATCH v5 2/4] dt-bindings: watchdog: add new binding for meson secure watchdog

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Hi, Guenter Martin

On 2019/12/16 21:30, Guenter Roeck wrote:
On 12/15/19 10:03 PM, Xingyu Chen wrote:
Hi, Martin

Sorry for the late reply.

On 2019/12/13 4:05, Martin Blumenstingl wrote:
Hi Xingyu and Rob,

On Thu, Dec 12, 2019 at 1:20 PM Xingyu Chen <xingyu.chen@xxxxxxxxxxx> wrote:
[...]
+examples:
+  - |
+    watchdog {
+          compatible = "amlogic,meson-sec-wdt";
+          timeout-sec = <60>;
+    };
in v3 of this patch Rob commented that there shouldn't be an OF node
if there are no additional properties
with timeout-sec there's now an additional property so my
understanding is that it's fine to have an OF node
Your understanding is correct.

what I don't understand yet is where this node should be placed.
is it supposed to be a child node of the secure monitor node (for
which we already have a binding here:
Documentation/devicetree/bindings/firmware/meson/meson_sm.txt) or
where else would we place it inside the .dts?
IMO,  Although the watchdog node need to reference the meson_sm node, there is no bus-like dependencies between the devices which the two nodes corresponding to. so i think that the watchdog node as child node of meson_sm maybe not appropriate.

The watchdog driver needs the meson SM's dt node, and it depends on the existence of that node. That seems enough of a relationship to warrant having it as child note.
Thanks for your reply, if i take the wdt node as child of secure monitor (sm), how should
i register or find the wdt device ?

I only think of the following three methods :
1). update the sm driver,and scan&register wdt device when the sm driver probes(It is like i2c), but there
are too many changes involved.

2). add "simple-bus" key string to compatible of sm node, and it will make the child node is registered as platform device, but it seems that the key string is not match current scene.

secure-monitor {
    compatible = "amlogic,meson-gxbb-sm",  "simple-bus";

    watchdog {
        compatible = "amlogic,meson-sec-wdt";
        timeout-sec = <60>;
    }
}

3).  don't register device, and find directly the watchdog node by using the of_* API in watchdog
driver (Eg: linux-4.x/drivers/tee/optee/core.c)

secure-monitor {
    compatible = "amlogic,meson-gxbb-sm";

    watchdog {
        compatible = "amlogic,meson-sec-wdt";
        timeout-sec = <60>;
    }
}

The method 3 looks better for me, do you have a better suggestion ? Thanks

BR

Guenter

.




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