linux-kernel - Re: [PATCH 1/3] mfd: apple-ibridge: Add Apple iBridge MFD driver.

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Message-ID: <20190609234951.GB16597@innovation.ch>
Date:   Sun, 9 Jun 2019 16:49:51 -0700
From:   "Life is hard, and then you die" <ronald@...ovation.ch>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-input@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mfd: apple-ibridge: Add Apple iBridge MFD driver.


On Tue, May 07, 2019 at 01:24:15PM +0100, Lee Jones wrote:
> On Sun, 21 Apr 2019, Ronald Tschalär wrote:
> 
> > The iBridge device provides access to several devices, including:
> > - the Touch Bar
> > - the iSight webcam
> > - the light sensor
> > - the fingerprint sensor
> > 
> > This driver provides the core support for managing the iBridge device
> > and the access to the underlying devices. In particular, since the
> > functionality for the touch bar and light sensor is exposed via USB HID
> > interfaces, and the same HID device is used for multiple functions, this
> > driver provides a multiplexing layer that allows multiple HID drivers to
> > be registered for a given HID device. This allows the touch bar and ALS
> > driver to be separated out into their own modules.
> > 
> > Signed-off-by: Ronald Tschalär <ronald@...ovation.ch>
> > ---
> >  drivers/mfd/Kconfig               |  15 +
> >  drivers/mfd/Makefile              |   1 +
> >  drivers/mfd/apple-ibridge.c       | 883 ++++++++++++++++++++++++++++++
> 
> I haven't taken a thorough look through, but I can tell you that the
> vast majority of what you're trying to do here does not belong in
> MFD.  MFD drivers are used to register child devices.  Almost all
> functionality or 'real work' should be contained in the drivers the
> MFD registers, not in the MFD parent itself.  You will need to move
> all 'real work' out into the subordinate device drivers for
> acceptance.

Thanks for your feedback. That was/is the idea: the actual Touch Bar
and ALS driver code is in separate modules - what is left in the
appple-ibridge mfd driver is a fairly generic hid driver
demultiplexer. However, that could be moved out into it's own
helper/module.

Having said that, it looks like the preference is to do all of this as
a hid driver with virtual hid devices instead of as an mfd driver.


  Cheers,

  Ronald