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

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Message-ID: <20190610054548.GD4797@dell>
Date:   Mon, 10 Jun 2019 06:45:48 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     "Life is hard, and then you die" <ronald@...ovation.ch>
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 Sun, 09 Jun 2019, Life is hard, and then you die wrote:

> 
> 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.

Sounds like a better approach.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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