linux-kernel - Re: [PATCH v3] watchdog: Add driver for Gunyah Watchdog

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Message-ID: <aa4faa81-6e9d-41c2-85f0-32045a8f9f51@kernel.org>
Date: Tue, 28 Oct 2025 17:40:33 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Pavan Kondeti <pavan.kondeti@....qualcomm.com>
Cc: Hrishabh Rajput <hrishabh.rajput@....qualcomm.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Wim Van Sebroeck <wim@...ux-watchdog.org>, Guenter Roeck
 <linux@...ck-us.net>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v3] watchdog: Add driver for Gunyah Watchdog

On 28/10/2025 17:33, Pavan Kondeti wrote:
> On Tue, Oct 28, 2025 at 05:17:44PM +0100, Krzysztof Kozlowski wrote:
>> On 28/10/2025 13:27, Pavan Kondeti wrote:
>>> On Tue, Oct 28, 2025 at 12:07:40PM +0100, Krzysztof Kozlowski wrote:
>>>> On 28/10/2025 12:04, Krzysztof Kozlowski wrote:
>>>>> On 28/10/2025 11:58, Hrishabh Rajput wrote:
>>>>>>
>>>>>> On 10/28/2025 3:10 PM, Krzysztof Kozlowski wrote:
>>>>>>> On 28/10/2025 10:35, Hrishabh Rajput via B4 Relay wrote:
>>>>>>>> +
>>>>>>>> +static int __init gunyah_wdt_init(void)
>>>>>>>> +{
>>>>>>>> +	struct arm_smccc_res res;
>>>>>>>> +	struct device_node *np;
>>>>>>>> +	int ret;
>>>>>>>> +
>>>>>>>> +	/* Check if we're running on a Qualcomm device */
>>>>>>>> +	np = of_find_compatible_node(NULL, NULL, "qcom,smem");
>>>>>>> I don't think you implemented my feedback. This again is executed on
>>>>>>> every platform, e.g. on Samsung, pointlessly.
>>>>>>>
>>>>>>> Implement previous feedback.
>>>>>>
>>>>>> Do you want us to add platform device from another driver which is 
>>>>>> probed only on Qualcomm devices (like socinfo from previous discussion) 
>>>>>> and get rid of the module init function entirely? As keeping anything in 
>>>>>> the module init will get it executed on all platforms.
>>>>>
>>>>> Instead of asking the same can you read previous discussion? What is
>>>>> unclear here:
>>>>> https://lore.kernel.org/all/3b901f9d-dbfa-4f93-a8d2-3e89bd9783c9@kernel.org/
>>>>> ?
>>>>>
>>>>>>
>>>>>>
>>>>>> With this patch version, we have tried to reduce the code execution on 
>>>>>> non-Qualcomm devices (also tried the alternative as mentioned in the 
>>>>>> cover letter). Adding platform device from another driver as described 
>>>>>> above would eliminate it entirely, please let us know if you want us to 
>>>>>> do that.
>>>>>
>>>>> Why do I need to repeat the same as last time?
>>>>
>>>>
>>>> Now I see that you completely ignored previous discussion and sent THE
>>>> SAME approach.
>>>
>>> Our intention is not to waste reviewers time at all. It is just a
>>> misunderstanding on what your comment is about. Let me elaborate further
>>> not to defend our approach here but to get a clarity so that we don't
>>> end up in the same situation when v4 is posted.
>>>
>>> https://lore.kernel.org/all/b94d8ca3-af58-4a78-9a5a-12e3db0bf75f@kernel.org/ 
>>>
>>> You mentioned here
>>>
>>> ```
>>> To me socinfo feels even better. That way only, really only qcom devices
>>> will execute this SMC.
>>> ```
>>>
>>> We interpreted this comment as `avoid executing this SMC on non qcom
>>> devices`. That is exactly what we have done in the current patch. since
>>
>>
>> So where did you use socinfo? Point me to the code.
>>
> 
> Okay, lets go a bit deep into the socinfo part. we have used
> `soc_device_match()` API to detect if the device is qcom (`family =
> Snapdragon`). It works. However, when we built both `socinfo` and

socinfo driver. Read my first feedback:


"No, your hypervisor driver (which you have) should start the module via
adding platform/aux/something devices."

And then I agreed if you start it from the socinfo driver.


> `gunyah-wdt` as modules, we do see that `gunyah-wdt` gets probed before
> `socinfo` because the driver that registers socinfo as platform device
> which is `smem` probe is getting delayed. As you may know `smem` device
> gets registered by `OF` core directly before the whole platform devices
> are populated. To make sure that any configuration works, we went with
> `qcom,smem` based detection. This is mentioned in the cover letter, sure
> it is a detail that can easily be lost. Now one might just say go and
> fix probe deferral problems. The problem here is that `smem` platform
> device creation happens differently to other devices which is leading to
> probe deferral. I can enumerate the problem in much detail, if that
> interests you.
> 
> Please help us understand what is the real concern here? we don't want
> to call `of_find_compatible_node()` API on non qcom devices but it is

It was told to you already multiple times and it is basic kernel
knowledge - you do not execute your init code on other platforms. At
all. You are developing like it was 2005. That was the style that time.

Write concise replies, I really have not much time to read LLM output.

Best regards,
Krzysztof