linux-kernel - Re: [PATCH v3 2/4] dt-bindings: watchdog: add new binding for meson secure watchdog

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Date:   Thu, 31 Oct 2019 20:40:44 +0800
From:   Xingyu Chen <xingyu.chen@...ogic.com>
To:     Rob Herring <robh@...nel.org>
CC:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Qianggui Song <qianggui.song@...ogic.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Jian Hu <jian.hu@...ogic.com>,
        LINUX-WATCHDOG <linux-watchdog@...r.kernel.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] dt-bindings: watchdog: add new binding for meson
 secure watchdog

Hi, Rob

On 2019/10/30 21:41, Rob Herring wrote:
> On Wed, Oct 30, 2019 at 7:59 AM Xingyu Chen <xingyu.chen@...ogic.com> wrote:
>>
>> Hi,Rob
>>
>> On 2019/10/30 4:51, Rob Herring wrote:
>>> On Mon, Oct 28, 2019 at 3:35 AM Xingyu Chen <xingyu.chen@...ogic.com> wrote:
>>>>
>>>> Hi, Rob
>>>>
>>>> On 2019/10/26 4:30, Rob Herring wrote:
>>>>> On Fri, Oct 25, 2019 at 02:13:02PM +0800, Xingyu Chen wrote:
>>>>>> The binding targets the Meson-A/C series compatible SoCs, in which the
>>>>>> watchdog registers are in secure world.
>>>>>>
>>>>>> Signed-off-by: Xingyu Chen <xingyu.chen@...ogic.com>
>>>>>> ---
>>>>>>     .../bindings/watchdog/amlogic,meson-sec-wdt.yaml   | 34 ++++++++++++++++++++++
>>>>>>     1 file changed, 34 insertions(+)
>>>>>>     create mode 100644 Documentation/devicetree/bindings/watchdog/amlogic,meson-sec-wdt.yaml
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/watchdog/amlogic,meson-sec-wdt.yaml b/Documentation/devicetree/bindings/watchdog/amlogic,meson-sec-wdt.yaml
>>>>>> new file mode 100644
>>>>>> index 00000000..0bbc807
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/watchdog/amlogic,meson-sec-wdt.yaml
>>>>>> @@ -0,0 +1,34 @@
>>>>>> +# SPDX-License-Identifier: (GPL-2.0+ OR MIT)
>>>>>> +# Copyright (c) 2019 Amlogic, Inc
>>>>>> +%YAML 1.2
>>>>>> +---
>>>>>> +$id: "http://devicetree.org/schemas/power/amlogic,meson-sec-wdt.yaml#"
>>>>>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>>>>>> +
>>>>>> +title: Amlogic Meson Secure Watchdog Timer
>>>>>> +
>>>>>> +maintainers:
>>>>>> +  - Xingyu Chen <xingyu.chen@...ogic.com>
>>>>>> +
>>>>>> +description: |+
>>>>>> +  Secure Watchdog Timer used in Meson-A/C series Compatible SoCs
>>>>>> +
>>>>>> +properties:
>>>>>> +  compatible:
>>>>>> +    enum:
>>>>>> +      - amlogic,meson-sec-wdt
>>>>>
>>>>> If there are no other properties, then you don't need this. Just have
>>>>> the secure firmware driver instantiate the watchdog.
>>>> I'am very sorry i don't understand how to initialize the watchdog driver
>>>> if the compatible property is removed, Could you give me more
>>>> suggestions or examples ？ Thank you very much.
>>>
>>> platform_device_register_simple() from the secure firmware driver.
>> Thanks for your help. The device node of wdt looks useless if I use this
>> function to register device. if so, how should I get the pointer to
>> secure-monitor in wdt driver ? or should I use directly arm_smccc to
>> access the secfw ?
> 
> You can use of_find_compatible_node(). There should only be one firmware node.
Thanks for your answer.

I seem to miss something about registration of watchdog device. The 
secure watchdog driver is used only to A1/C1 compatible SoCs, but is not
support for previous SoCs (Eg: gxl axg).

I have to think about platform difference If I use the 
platform_device_register_simple() to register the wdt device in secure
fw driver, because fw driver is compatible with all known SoCs, but the 
secure wdt driver is only compatible with some SoCs. In other
words, the registered wdt device is useless for gxl or axg.

There is no such problem If I use the DT to describe the wdt device.

> 
> Rob
> 
> .
>