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

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Date: Tue, 23 Jan 2024 09:02:35 +0200
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Guenter Roeck <linux@...ck-us.net>, 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 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.

[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?

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
>