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

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Date: Tue, 23 Jan 2024 02:09:27 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: claudiu beznea <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
Cc: 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 23:13, claudiu beznea wrote:
> 
> 
> On 22.01.2024 19:39, 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.
> 
> The necessity of __maybe_unused has been removed along with the
> introduction of LATE_SYSTEM_SLEEP_PM_OPS() and friends (and
> *SET_*LATE_SYSTEM_SLEEP_PM_OPS along with the other helpers were marked
> deprecated for that) and we can use pm_ptr() along with
> LATE_SYSTEM_SLEEP_PM_OPS() to avoid build errors you mentioned.
> 
> FYI, I just build the driver with CONFIG_PM=n and all good.
> 

Ok, but are you sure you did ? You just mentioned earlier that CONFIG_PM
is set automatically through ARCH_RZG2L.

>> 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.
> 
> That's true. The driver wouldn't work if the CONFIG_PM=n but then it
> depends on COMPILE_TEST which is exactly for this (just to compile test it
> for platforms that don't support it). I see many watchdog drivers depends
> on COMPILE_TEST.
> 
> Give this, please let me know would you like me to proceed with it.
> 

FWIW, COMPILE_TEST dependencies on watchdog drivers fails for most of them.
Regarding pm_ptr(), it is there for practical reasons and not associated with
COMPILE_TEST. Again, if the driver depends on CONFIG_PM to work, using constructs
such as pm_ptr() just hides that and creates the impression that it would work
without it. I do not think that is a good idea. You can use something like

	depends on (ARCH_RENESAS && PM) || COMPILE_TEST

to make that explicit. Even if not, I _really_ don't see the point in using
pm_ptr() even without above dependency. What do you see as its benefit ?

Thanks,
Guenter

> Thank you,
> Claudiu Beznea
> 
>>
>> 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
>>
>>>        },
>>>        .probe = rzg2l_wdt_probe,
>>>    };
>>