linux-kernel - Re: Simple MFD driver example

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Message-ID: <CAOMwXhMn5W76Dp=EFNHaknXCqZ4q4e7fphgtttx+8U=1Fc_DMQ@mail.gmail.com>
Date:	Mon, 16 Dec 2013 16:39:52 +0000
From:	Laszlo Papp <lpapp@....org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	sameo@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Simple MFD driver example

On Mon, Dec 16, 2013 at 3:05 PM, Lee Jones <lee.jones@...aro.org> wrote:
> Please refrain from top posting.
>
> Responses should appear under quoted lines, which they reference.

I intentionally did not reply to a specific quote, but to the email as a whole!

>> >> I have been trying to write about 50-100 LOC for 1-2 weeks now. I have
>> >> a fairly simple use case for MFD where I need to have gpio and hwmon
>> >> functionality for a GPIO.
>> >>
>> >> I read the mfd drivers inside and out by now, but it looks a bit
>> >> inconsistent to me. I am not sure what to follow etc. The
>> >> documentation seems to be virtually missing which makes my life and
>> >> involvement even more difficult. :(
>> >>
>> >> May I ask for some pointer how to do all this? It would be nice to see
>> >> a minimal example where the parent does not do anything else than just
>> >> enumerating the sub-device drivers. Is that possible with an empty
>> >> probe callback?
>> >>
>> >> If I understand the regmap correctly (again, it is possible I do not),
>> >> then I would not need this. But in general, it is really hard to deal
>> >> with the linux kernel in this regard when basic documentations are
>> >> missing.
>> >>
>> >> I hope this would change over time for the posterity. It is a pity
>> >> that contributors do not join probably due to this. It is a bit
>> >> chaotic, but I hope it can be changed in the future.
>> >>
>> >> Apologies for my frustration...
>> >
>> > Due to the nature of the MFD subsystem, there isn't a simple use-case
>> > which you can use as a template. It's completely dependent on the
>> > device you are trying to enable. There are lots of well written
>> > drivers in the subsystem that you can use as good examples though.
>
>> Well, if you ask me the MFD subsystem is underdocumented, and there is
>> some inconsistency between the drivers. It is hard to take any of them
>> as a starting point, at least for me.
>
> Feel free to write some. I'm always happy to take helpful patches.

I am not the right person for documentating everything here,
especially when I do not even understand basics... I am just trying to
figure out my way here. It was more like a hint that this area could
take some love. At least, I would personally appreciate it a lot. It
is currently somewhat difficult to get involved.
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