linux-kernel - Re: [PATCH 03/10] watchdog: rzg2l_wdt: Check return status of pm_runtime

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Date: Tue, 23 Jan 2024 02:00:22 -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 03/10] watchdog: rzg2l_wdt: Check return status of
 pm_runtime_put()

On 1/22/24 23:02, claudiu beznea wrote:
> 
> 
> On 22.01.2024 19:31, Guenter Roeck wrote:
>> On 1/22/24 03:11, Claudiu wrote:
>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>
>>> pm_runtime_put() may return an error code. Check its return status.
>>>
>>> Fixes: 2cbc5cd0b55f ("watchdog: Add Watchdog Timer driver for RZ/G2L")
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>> ---
>>>    drivers/watchdog/rzg2l_wdt.c | 6 +++++-
>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c
>>> index 4ab9e7c5e771..0554965027cd 100644
>>> --- a/drivers/watchdog/rzg2l_wdt.c
>>> +++ b/drivers/watchdog/rzg2l_wdt.c
>>> @@ -144,9 +144,13 @@ static int rzg2l_wdt_start(struct watchdog_device
>>> *wdev)
>>>    static int rzg2l_wdt_stop(struct watchdog_device *wdev)
>>>    {
>>>        struct rzg2l_wdt_priv *priv = watchdog_get_drvdata(wdev);
>>> +    int ret;
>>>          rzg2l_wdt_reset(priv);
>>> -    pm_runtime_put(wdev->parent);
>>> +
>>> +    ret = pm_runtime_put(wdev->parent);
>>> +    if (ret < 0)
>>> +        return ret;
>>>          return 0;
>>>    }
>>
>> A simple
>>      return pm_runtime_put();
>> might do.
> 
> pm_runtime_put() may return 1 if the device is already suspended though
> this call trace:
> 
> pm_runtime_put() ->
>     __pm_runtime_idle() ->
>         rpm_idle() ->
>             rpm_suspend() ->
>                 rpm_check_suspend_allowed() [1]
> 
> That return value is not considered error thus I wanted to consider it
> here, too.
> 
Good point.

> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/base/power/runtime.c#L278
> 
>>
>> However, one question: Given that pm_runtime_put() returns -ENOSYS if
>> CONFIG_PM is disabled, that means the driver will depend on CONFIG_PM=y.
> 
> Indeed, the driver depends on CONFIG_PM=y for proper working. It is for
> devices selecting ARCH_RZG2L and RZ/V2M (ARM64 based uarch) which select
> CONFIG_PM=y:
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/renesas/Kconfig#L45
> 
> The driver is written with CONFIG_PM=y dependency in mind (e.g. the clocks
> are enabled though runtime PM APIs).
> 
>> Assuming this is intentional, would it make sense to explicitly declare
>> that dependency in Kconfig ? It doesn't seem to make any sense to build
>> the driver if it won't work anyway.
> 
> The dependency exists there for ARCH_RZG2L and RZ/V2M devices but not
> directly and it is not strict (in the sense that we allow to build the
> driver w/o CONFIG_PM (I think this is good to check build on different
> configurations, the COMPILE_TEST is there anyway in [1]) ). E.g.:
> 
> RENESAS_RZG2LWDT depends on ARCH_RENESAS [1]
> ARCH_RENESAS is the ARMv8 uarch flag [2]
> SOC_RENESAS is set if ARCH_RENESAS [3]
> ARCH_RZG2L is visible only if SOC_RENESAS [4]
> ARCH_RZG2L selects PM [5]
> RZ/V2M selects PM [6]
> 
> Please let me know what do you think about it?
> 
If the driver indeed depends on CONFIG_PM, that should be made explicit.

Guenter

> Thank you,
> Claudiu Beznea
> 
> 
> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/watchdog/Kconfig#L913
> [2]
> https://elixir.bootlin.com/linux/latest/source/arch/arm64/Kconfig.platforms#L273
> [3]
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/renesas/Kconfig#L2
> [4]
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/renesas/Kconfig#L9
> [5]
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/renesas/Kconfig#L45
> [6]
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/renesas/Kconfig#L328
> 
> 
>>
>> Thanks,
>> Guenter
>>
>