linux-kernel - Re: Simple MFD driver example

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Message-ID: <20131218113449.GF14274@lee--X1>
Date:	Wed, 18 Dec 2013 11:34:49 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Laszlo Papp <lpapp@....org>
Cc:	sameo@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: Simple MFD driver example

> >> What you eventually see in hwmon is only a subset of all the features
> >> the IC provides. You may want to read this thread:
> >> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg536509.html
> >
> > Okay, so the best thing to do is send out the entire patch-set at
> > once, CC'ing each of the maintainers on every patch so we can all see
> > how this thing fits together.
> 
> Well, I am not even sure currently where to head with the MFD bits and
> its children subdevices currently....
> 
> I would appreciate any direction. Yesterday, I was told on IRC, I
> would need to switch from i2c to platform drivers for the hwmon and
> gpio parts, but looking at some existing mfd driver code and their
> children drivers, I do not see it like that.
> 
> I have already sent out the gpio driver yesterday which works fine on
> its own: http://www.spinics.net/lists/kernel/msg1655805.html

This is going to need a lot of work.

Did you run the patch through `./scripts/checkpatch.pl` before
submitting?

> Could you please guide me into the right direction what I need to
> change once we have standalone drivers, and they should be glued
> together? I thought adding an abstraction with the mfd layer would be
> sufficient, but apparently, that is not enough.
> 
> Practically speaking, I am confused since if I needed to change the
> existing drivers, that means I could potentially break the interface
> for the existing users if the drivers stop working on their own, but
> then again, I am such a newbie that I would greatly appreciate some
> pointers.

The MFD subsystem is quite simple to use. I'm taken aback that this is
your major stumbling block. Read though the mfd_add_device(s)() calls
to see what it expects. The rest is childs play.

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