Re: [PATCH v4 1/2] soc: qcom: smem: Register gunyah watchdog device

[Hrishabh Rajput <hrishabh.rajput@oss.qualcomm.com>]

On 11/2/2025 12:20 AM, Bjorn Andersson wrote:
> On Fri, Oct 31, 2025 at 08:24:44AM -0700, Guenter Roeck wrote:
>> On 10/31/25 03:18, Hrishabh Rajput via B4 Relay wrote:
>>> From: Hrishabh Rajput <hrishabh.rajput@oss.qualcomm.com>
>>>
>>> To restrict gunyah watchdog initialization to Qualcomm platforms,
>>> register the watchdog device in the SMEM driver.
>>>
>>> When Gunyah is not present or Gunyah emulates MMIO-based
>>> watchdog, we expect Qualcomm watchdog or ARM SBSA watchdog device to be
>>> present in the devicetree. If none of these device nodes are detected,
>>> we register the SMC-based Gunyah watchdog device.
>>>
>> There should also be an explanation why there is no "qcom,gunyah-wdt"
>> devicetree node, both here and in the file.
>>
>>> Signed-off-by: Hrishabh Rajput <hrishabh.rajput@oss.qualcomm.com>
>>> ---
>>>    drivers/soc/qcom/smem.c | 37 +++++++++++++++++++++++++++++++++++++
>>>    1 file changed, 37 insertions(+)
>>>
>>> diff --git a/drivers/soc/qcom/smem.c b/drivers/soc/qcom/smem.c
>>> index cf425930539e..40e4749fab02 100644
>>> --- a/drivers/soc/qcom/smem.c
>>> +++ b/drivers/soc/qcom/smem.c
>>> @@ -1118,6 +1118,34 @@ static int qcom_smem_resolve_mem(struct qcom_smem *smem, const char *name,
>>>    	return 0;
>>>    }
>>> +static int register_gunyah_wdt_device(void)
>>> +{
>>> +	struct platform_device *gunyah_wdt_dev;
>>> +	struct device_node *np;
>>> +
>>> +	/*
>>> +	 * When Gunyah is not present or Gunyah is emulating a memory-mapped
>>> +	 * watchdog, either of Qualcomm watchdog or ARM SBSA watchdog will be
>>> +	 * present. Skip initialization of SMC-based Gunyah watchdog if that is
>>> +	 * the case.
>>> +	 */
>>> +	np = of_find_compatible_node(NULL, NULL, "qcom,kpss-wdt");
>>> +	if (np) {
>>> +		of_node_put(np);
>>> +		return 0;
>>> +	}
>>> +
>>> +	np = of_find_compatible_node(NULL, NULL, "arm,sbsa-gwdt");
>>> +	if (np) {
>>> +		of_node_put(np);
>>> +		return 0;
>>> +	}
>>> +
>>> +	gunyah_wdt_dev = platform_device_register_simple("gunyah-wdt", -1,
>>> +							 NULL, 0);
>>> +	return PTR_ERR_OR_ZERO(gunyah_wdt_dev);
>>> +}
>>> +
>>>    static int qcom_smem_probe(struct platform_device *pdev)
>>>    {
>>>    	struct smem_header *header;
>>> @@ -1236,11 +1264,20 @@ static int qcom_smem_probe(struct platform_device *pdev)
>>>    	if (IS_ERR(smem->socinfo))
>>>    		dev_dbg(&pdev->dev, "failed to register socinfo device\n");
>>> +	ret = register_gunyah_wdt_device();
>>> +	if (ret)
>>> +		dev_dbg(&pdev->dev, "failed to register watchdog device\n");
>>> +
>>>    	return 0;
>>>    }
>>>    static void qcom_smem_remove(struct platform_device *pdev)
>>>    {
>>> +	/*
>>> +	 * Gunyah watchdog is intended to be a persistent module. Hence, the
>>> +	 * watchdog device is not unregistered.
>>> +	 */
>>> +
>> Odd explanation.
>> I would assume that the smem device is supposed to be
>> persistent as well.
> Yes, but it's perfectly possible to run a modern Qualcomm device without
> SMEM, with a fair amount of functionality. So, the reevaluation of this
> decision is grinding in the back of my mind...

One option can be the SCM driver which was suggested by Neil in v3 [1].

Let us know if you have any suggestions where we can register the 
watchdog device?

[1]: 
https://lore.kernel.org/lkml/321f5289-64c0-48f1-91b5-c45e82396ca9@linaro.org/

Thanks,

Hrishabh