linux-kernel - Re: [PATCH 07/10] watchdog: rzg2l

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Date: Mon, 22 Jan 2024 14:00:16 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Jerry.Hoemann@....com
Cc: Claudiu <claudiu.beznea@...on.dev>, wim@...ux-watchdog.org,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 geert+renesas@...der.be, magnus.damm@...il.com, mturquette@...libre.com,
 sboyd@...nel.org, p.zabel@...gutronix.de, biju.das.jz@...renesas.com,
 linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-clk@...r.kernel.org, Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 07/10] watchdog: rzg2l_wdt: Add suspend/resume support

On 1/22/24 13:05, Jerry Hoemann wrote:
> On Mon, Jan 22, 2024 at 09:39:27AM -0800, Guenter Roeck wrote:
>> On 1/22/24 03:11, Claudiu wrote:
>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>
>>> The RZ/G3S supports deep sleep states where power to most of the IP blocks
>>> is cut off. To ensure proper working of the watchdog when resuming from
>>> such states, the suspend function is stopping the watchdog and the resume
>>> function is starting it. There is no need to configure the watchdog
>>> in case the watchdog was stopped prior to starting suspend.
>>>
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>> ---
>>>    drivers/watchdog/rzg2l_wdt.c | 26 ++++++++++++++++++++++++++
>>>    1 file changed, 26 insertions(+)
>>>
>>> diff --git a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c
>>> index 9333dc1a75ab..186796b739f7 100644
>>> --- a/drivers/watchdog/rzg2l_wdt.c
>>> +++ b/drivers/watchdog/rzg2l_wdt.c
>>> @@ -279,6 +279,7 @@ static int rzg2l_wdt_probe(struct platform_device *pdev)
>>>    	priv->wdev.timeout = WDT_DEFAULT_TIMEOUT;
>>>    	watchdog_set_drvdata(&priv->wdev, priv);
>>> +	dev_set_drvdata(dev, priv);
>>>    	ret = devm_add_action_or_reset(&pdev->dev, rzg2l_wdt_pm_disable, &priv->wdev);
>>>    	if (ret)
>>>    		return ret;
>>> @@ -300,10 +301,35 @@ static const struct of_device_id rzg2l_wdt_ids[] = {
>>>    };
>>>    MODULE_DEVICE_TABLE(of, rzg2l_wdt_ids);
>>> +static int rzg2l_wdt_suspend_late(struct device *dev)
>>> +{
>>> +	struct rzg2l_wdt_priv *priv = dev_get_drvdata(dev);
>>> +
>>> +	if (!watchdog_active(&priv->wdev))
>>> +		return 0;
>>> +
>>> +	return rzg2l_wdt_stop(&priv->wdev);
>>> +}
>>> +
>>> +static int rzg2l_wdt_resume_early(struct device *dev)
>>> +{
>>> +	struct rzg2l_wdt_priv *priv = dev_get_drvdata(dev);
>>> +
>>> +	if (!watchdog_active(&priv->wdev))
>>> +		return 0;
>>> +
>>> +	return rzg2l_wdt_start(&priv->wdev);
>>> +}
>>> +
>>> +static const struct dev_pm_ops rzg2l_wdt_pm_ops = {
>>> +	LATE_SYSTEM_SLEEP_PM_OPS(rzg2l_wdt_suspend_late, rzg2l_wdt_resume_early)
>>> +};
>>> +
>>>    static struct platform_driver rzg2l_wdt_driver = {
>>>    	.driver = {
>>>    		.name = "rzg2l_wdt",
>>>    		.of_match_table = rzg2l_wdt_ids,
>>> +		.pm = pm_ptr(&rzg2l_wdt_pm_ops),
>>
>> I think this will create a build error if CONFIG_PM=n because rzg2l_wdt_pm_ops
>> will be unused but is not marked with __maybe_unused. But then the driver won't be
>> operational with CONFIG_PM=n, so I really wonder if it makes sense to include any
>> such conditional code instead of making the driver depend on CONFIG_PM.
>>
>> I really don't think it is desirable to suggest that the driver would work with
>> CONFIG_PM=n if that isn't really true.
>>
>> Guenter
> 
> Guenter,
> 
> I'm working on a similar patch.
> 
> Is your concern limited to the use of the "pm_ptr" macro?  Or is it
> wider?
> 

patch 3/10 adds an error check of the return value from pm_runtime_put().
pm_runtime_put() calls __pm_runtime_idle() which returns -ENOSYS if
CONFIG_PM=n. That means checking the return value of pm_runtime_put()
is equivalent to making CONFIG_PM mandatory. My argument is that this
should be expressed in Kconfig to avoid the impression that the driver
works with CONFIG_PM=n. If the driver depends on CONFIG_PM, pm_ptr()
is unnecessary. If it doesn't, the variable referenced by it needs
to be defined as __maybe_unused, but then the driver should actually
work with CONFIG_PM=n.

Yes, I have noticed the recent trend of adding error checks to
pm_runtime_put(), but I only now realized that it has consequences.

Guenter