Re: [PATCH v7 05/10] mfd: Add Apple Silicon System Management Controller

[Sven Peter <sven@kernel.org>]

On 24.06.25 17:53, Lee Jones wrote:
> On Sat, 21 Jun 2025, Sven Peter wrote:
> 
>> On 19.06.25 13:49, Lee Jones wrote:
>>> On Tue, 10 Jun 2025, Sven Peter wrote:
>>>
>>>> The System Management Controller (SMC) on Apple Silicon machines is a
>>>> piece of hardware that exposes various functionalities such as
>>>> temperature sensors, voltage/power meters, shutdown/reboot handling,
>>>> GPIOs and more.
>>>>
>>>> Communication happens via a shared mailbox using the RTKit protocol
>>>> which is also used for other co-processors. The SMC protocol then allows
>>>> reading and writing many different keys which implement the various
>>>> features. The MFD core device handles this protocol and exposes it
>>>> to the sub-devices.
>>>>
>>>> Some of the sub-devices are potentially also useful on pre-M1 Apple
>>>> machines and support for SMCs on these machines can be added at a later
>>>> time.
>>>>
>>>> Co-developed-by: Hector Martin <marcan@marcan.st>
>>>> Signed-off-by: Hector Martin <marcan@marcan.st>
>>>> Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
>>>> Reviewed-by: Neal Gompa <neal@gompa.dev>
>>>> Signed-off-by: Sven Peter <sven@kernel.org>
>>>> ---
>>>>    MAINTAINERS                |   2 +
>>>>    drivers/mfd/Kconfig        |  18 ++
>>>>    drivers/mfd/Makefile       |   1 +
>>>>    drivers/mfd/macsmc.c       | 498 +++++++++++++++++++++++++++++++++++++++++++++
>>>>    include/linux/mfd/macsmc.h | 279 +++++++++++++++++++++++++
>>>>    5 files changed, 798 insertions(+)
>>>
>>> This is ready.  Let me know when you have all of the other driver/* Acks.
>>>
>>
>> They've all been reviewed by the respective maintainers.
>>
>> I assume you want to take this all through the mfd tree and we'll need acks
>> from Sebastian for power/reset and either Linus or Bartosz for gpio then.
> 
> That's right.

Can you maybe comment on 
https://lore.kernel.org/asahi/20250610-smc-6-15-v7-0-556cafd771d3@kernel.org/T/#m25fe0bd8fe5fa47ed63f4238da80d7186a65450c?

A sub device declared with

MFD_CELL_OF("macsmc-reboot", NULL, NULL, 0, 0, "apple,smc-reboot")

is picked up even if there's no corresponding node in the device tree.
Is this expected behavior for mfd? There are some pre-M1 iDevices that 
also have a variant of SMC that doesn't have the reboot functionality.
We can always special case it with a different compatible but just 
dropping the sub-node from the device tree would've been neat.

> 
>> The one line change inside drivers/soc/apple would usually go through my
>> tree and I'm fine with taking that through mfd instead.
> 
> If there are no build-time dependencies on it, you can take it.

Okay, I've picked it up now.

> 
> I'm happy to take only the inter-dep ones or all (except the arch/ ones).
>

Sure, I'll take those as well once the dt-bindings are in.


Thanks,

Sven