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

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Message-Id: <201612281005.22088@pali>
Date:   Wed, 28 Dec 2016 10:05:21 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Valdis.Kletnieks@...edu,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Jean Delvare <jdelvare@...e.com>,
        Steven Honeyman <stevenhoneyman@...il.com>,
        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>,
        MichaÅ‚ KÄ™pieÅ„ 
        <kernel@...pniu.pl>, Takashi Iwai <tiwai@...e.de>,
        linux-i2c@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] i2c: i801: Register optional lis3lv02d i2c device on Dell machines

On Wednesday 28 December 2016 08:55:18 Andy Shevchenko wrote:
> On Wed, Dec 28, 2016 at 12:41 AM,  <Valdis.Kletnieks@...edu> wrote:
> > On Wed, 28 Dec 2016 00:15:30 +0200, Andy Shevchenko said:
> >> On Tue, Dec 27, 2016 at 3:51 PM, Pali Rohár <pali.rohar@...il.com> wrote:
> >
> >> > I have no idea how to do it (properly) outside of i2c-i801.c file.
> >>
> >> I doubt we need a single line of code for this. See [1] and perhaps
> >> create an EFI variable with necessary upgrade device node.
> >>
> >> > Same thing is done for Fujitsu machines, see function
> >> > i801_probe_optional_slaves() in i2c-i801.c file. So I did similar
> >> > approach for Dell machines.
> >>
> >> Perhaps, this also needs to be converted to use EFI variable.
> >>
> >> [1] https://lwn.net/Articles/693212/
> >
> > There's no guarantee that the laptops in question are booted with UEFI,
> > as Dell still supports legacy boot. So assuming the presence of EFI variables
> > is somewhat problematic.
> 
> 
> > In addition, it requires the user (or something in userspace) to set the UEFI
> > variable or configfs tweak, rather than Just Working Out Of The Box.
> 
> I have no strong opinion, though I don't support the idea to put all
> hacks in the world to the kernel. For example, we have user space tool
> to switch USB modem from storage to actual communication device and
> that is just working out of the box.
> 
> Mika, Darren, what are your opinions?

I have absolutely no idea how to you want to achieve calling that i2c_new_device() registration 
without kernel patches.

So before starting discussion which option to use (EFI, kernel patch, userspace script, etc...) 
please describe how would you implement such logic with different options.

-- 
Pali Rohár
pali.rohar@...il.com

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