linux-kernel - Re: Simple MFD driver example

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Message-ID: <20131216164844.GS18769@lee--X1>
Date:	Mon, 16 Dec 2013 16:48:44 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Laszlo Papp <lpapp@....org>
Cc:	sameo@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Simple MFD driver example

> > 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!

Then you should have placed your response underneath the whole email,
not on top. If you're going to continue contributing to Mainline,
please find yourself a better email client. I assume you're using
Gmail at the moment, which is not suitable for this purpose.

> >> >> 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.

There isn't any documentation that would help you I fear. I'm trying
to help you, but you haven't answered my previous question.

Do you have a datasheet for the device that you're trying to enable?

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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