linux-kernel - Re: [PATCH] i2c: i801: Register optional lis3lv02d i2c device on Dell machines

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Date:   Wed, 4 Jan 2017 12:35:00 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Michał Kępień <kernel@...pniu.pl>,
        Jean Delvare <jdelvare@...e.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Steven Honeyman <stevenhoneyman@...il.com>,
        Valdis Kletnieks <Valdis.Kletnieks@...edu>,
        Jochen Eisinger <jochen@...guin-breeder.org>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Mario Limonciello <Mario_Limonciello@...l.com>,
        Alex Hung <alex.hung@...onical.com>,
        Takashi Iwai <tiwai@...e.de>, linux-i2c@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH] i2c: i801: Register optional lis3lv02d i2c device on
 Dell machines

On Wednesday 04 January 2017 11:25:44 Benjamin Tissoires wrote:
> On Jan 04 2017 or thereabouts, Andy Shevchenko wrote:
> > On Tue, Jan 3, 2017 at 10:39 PM, Pali Rohár <pali.rohar@...il.com> wrote:
> > >
> > > With Michał we already discussed about it, see emails. Basically you can
> > > enable/disable kernel modules at compile time or blacklist at runtime
> > > (or even chose what will be compiled into vmlinux and what as external
> > > .ko module). Some distributions blacklist i2c-i801.ko module...
> > 
> > But you understand that any of compile/not compile is not an option, right?
> > The case which we face will be both of them, if possible, will be
> > compiled as modules.
> > 
> > Blacklisting means making your problem the actual user's one. Not good.
> > 
> > > And
> > > there can be also problem with initialization of i2c-i801 driver (fix is
> > > in commit a7ae81952cda, but does not have to work at every time!). So
> > > that move on whitelisted machines can potentially cause disappearance of
> > > /dev/freefall and users will not have hdd protection which is currently
> > > working.
> > 
> 
> I am seeing the same issues with psmouse and SMBus touchpads. The PS/2
> device knows about the availability of a better but unlisted device at
> the ACPI level.
> 
> The way I solved this to not have to deal with compile/not compile and
> runtime errors is the same way Wolfram told you about: bus notifiers.
> I also use an intermediate platform driver to not add i2c dependency on
> psmouse.
> 
> For you the solution would be:
> - In dell-smo8800, after checking the whitelist, add a platform driver
>   "dell-lis3lv02d-platform", and add in the platform_data the I2C address
>   of the chip.
> - create a new driver dell-lis3lv02d-platform.ko which listens for the
>   i2c bus creation and registers the lis3lv02d I2C node when it sees a
>   matching adapter. (see [1] for my solution)
> - in dell-lis3lv02d-platform.ko make sure to set the irq to -ENOENT so
>   that lis3lv02d.ko doesn't create /dev/freefall which will still be
>   handled by ACPI.
> 
> How does that sound?

Yes, something like this was already suggested. But it is more
complicated as my approach and less error prone... See my notes in
previous emails.

My current path (after fixing IRQ to -1) is smaller more intuitive and
do not introduce new complicated parts like bus notifier and new "fake"
i2c driver...

> Cheers,
> Benjamin
> 
> [1] https://github.com/bentiss/linux/blob/synaptics-rmi4-v4.9-rc7+/drivers/input/rmi4/rmi_platform.c 

-- 
Pali Rohár
pali.rohar@...il.com