linux-kernel - Re: [PATCH v4 3/3] rtc: spacemit: default module when MFD_SPACEMIT

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Message-ID: <6ca28183-1687-4ddc-8b3c-5e5be4255561@riscstar.com>
Date: Mon, 29 Dec 2025 19:46:59 -0600
From: Alex Elder <elder@...cstar.com>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: Troy Mitchell <troy.mitchell@...ux.spacemit.com>,
 Lee Jones <lee@...nel.org>, Yixun Lan <dlan@...too.org>,
 Andi Shyti <andi.shyti@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
 linux-i2c@...r.kernel.org, linux-rtc@...r.kernel.org
Subject: Re: [PATCH v4 3/3] rtc: spacemit: default module when MFD_SPACEMIT_P1
 is enabled

On 12/29/25 6:51 PM, Alexandre Belloni wrote:
> On 29/12/2025 12:02:23-0600, Alex Elder wrote:
>> On 12/25/25 10:53 AM, Alexandre Belloni wrote:
>>> On 25/12/2025 15:46:33+0800, Troy Mitchell wrote:
>>>> The RTC driver defaulted to the same value as MFD_SPACEMIT_P1, which
>>>> caused it to be built-in automatically whenever the PMIC support was
>>>> set to y.
>>>>
>>>> This is not always desirable, as the RTC function is not required on
>>>> all platforms using the SpacemiT P1 PMIC.
>>>
>>> But then, can't people simply change the config? I don't feel like
>>> this is an improvement.
>>
>> It's not an improvement for people who want to use the SpacemiT
>> P1 PMIC, but it's an improvement for all the other RISC-V builds
>> using "defconfig" that would rather have that support be modular
>> to avoid needlessly consuming resources.
> 
> But then, wouldn't MFD_SPACEMIT_P1 be simply not set or set to m ? So
> this doesn't have any impact on other RISC-V builds while it makes
> people using the SpacemiT P1 PMIC jump through hoops to be able to use
> the RTC as this is a very uncommon way to set default values.
> 
> My point is:
>   - other RISC-V platforms would simply not select MFD_SPACEMIT_P1 or
>     have MFD_SPACEMIT_P1 set to m
>   - having RTC_DRV_SPACEMIT_P1 built-in by default when MFD_SPACEMIT_P1
>     is built-in doesn't really hurt any SpacemiT P1 users but would be
>     the expectation of those using the RTC.

The "hurt" isn't about P1 users, it's about everyone else.

>   - those wanting to optimise because they won't use the RTC, they can
>     already simply unselect RTC_DRV_SPACEMIT_P1 or set it to m.


The purpose is to make the driver a module (not built-in)
when "defconfig" is used (without the need for any Kconfig
fragments to unselect things).


In arch/riscv/configs/defconfig, we have this:
     CONFIG_ARCH_SPACEMIT=y

In drivers/mfd/Kconfig b/drivers/mfd/Kconfig, we have this
(added by patch 2 in this series):
     config MFD_SPACEMIT_P1
	default m if ARCH_SPACEMIT

So when using defconfig (alone), MFD_SPACEMIT_P1 is set to m,
to benefit non-SpacemiT RISC-V platforms.

This patch is trying to do the same thing for the RTC,
i.e. having RTC_DRV_SPACEMIT_P1 be defined as a module
by default.

I think you understand.

					-Alex
>> I haven't done any testing on this but it looks fine to me.
>>
>> Acked-by: Alex Elder <elder@...cstar.com>
>>
>> I think it's a small change worth merging.  I don't think
>> doing so does any harm.  Your call or course, Alexandre.
>>
>> 					-Alex
>>
>>>> Signed-off-by: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
>>>> ---
>>>>    drivers/rtc/Kconfig | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
>>>> index 50dc779f7f983074df7882200c90f0df21d142f2..53866493e9bbaf35ff0de85cbfe43e8343eadc1e 100644
>>>> --- a/drivers/rtc/Kconfig
>>>> +++ b/drivers/rtc/Kconfig
>>>> @@ -410,7 +410,7 @@ config RTC_DRV_SPACEMIT_P1
>>>>    	tristate "SpacemiT P1 RTC"
>>>>    	depends on ARCH_SPACEMIT || COMPILE_TEST
>>>>    	depends on MFD_SPACEMIT_P1
>>>> -	default MFD_SPACEMIT_P1
>>>> +	default m if MFD_SPACEMIT_P1
>>>>    	help
>>>>    	  Enable support for the RTC function in the SpacemiT P1 PMIC.
>>>>    	  This driver can also be built as a module, which will be called
>>>>
>>>> -- 
>>>> 2.52.0
>>>>
>>>
>>
>