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

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Date:   Thu, 19 Dec 2019 10:51:04 +0800
From:   Xingyu Chen <xingyu.chen@...ogic.com>
To:     Rob Herring <robh@...nel.org>
CC:     Guenter Roeck <linux@...ck-us.net>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Qianggui Song <qianggui.song@...ogic.com>,
        <devicetree@...r.kernel.org>, <linux-watchdog@...r.kernel.org>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        <linux-kernel@...r.kernel.org>, Jian Hu <jian.hu@...ogic.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [PATCH v5 2/4] dt-bindings: watchdog: add new binding for meson
 secure watchdog

Hi, Rob

On 2019/12/19 4:34, Rob Herring wrote:
> On Wed, Dec 18, 2019 at 03:37:49PM +0800, Xingyu Chen wrote:
>> 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@...ogic.com> 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.
> Just add of_platform_default_populate() call and clean-up calls. That's
> not what I'd call 'too many changes'.
Thanks for your guidance.
>
>   
>> 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.
> You previously said it's not a bus...
>
>> 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
>>>
>>> .
>>>
> .
>