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

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Message-ID: <wxdglhtsss4it6gfm3d7nngi6aezcvpcs44oa5mlmdwe34d5o2@qlkri6oknnpe>
Date: Sat, 1 Nov 2025 13:50:47 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: hrishabh.rajput@....qualcomm.com, 
	Konrad Dybcio <konradybcio@...nel.org>, Wim Van Sebroeck <wim@...ux-watchdog.org>, 
	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, 
	Pavan Kondeti <pavan.kondeti@....qualcomm.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Subject: Re: [PATCH v4 1/2] soc: qcom: smem: Register gunyah watchdog device

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@....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@....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...

Regards,
Bjorn

> Since  that is not the case, what happens if _this_
> device is unregistered and registered again ?
> 
> Guenter
> 
> >   	platform_device_unregister(__smem->socinfo);
> >   	hwspin_lock_free(__smem->hwlock);
> > 
>