linux-kernel - Re: [PATCH v4] platform/x86: ideapad-laptop: Add sysfs interface for touchpad state

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Message-ID: <20170503161104.GA30927@fury>
Date:   Wed, 3 May 2017 09:11:04 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Ritesh Raj Sarraf <rrs@...ian.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Ike Panhc <ike.pan@...onical.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] platform/x86: ideapad-laptop: Add sysfs interface for
 touchpad state

On Wed, May 03, 2017 at 05:42:02PM +0300, Andy Shevchenko wrote:
> On Wed, May 3, 2017 at 5:36 PM, Ritesh Raj Sarraf <rrs@...ian.org> wrote:
> > Resending again, as Google servers are behaving weird lately.
> >
> > On Sun, 2017-04-30 at 15:54 +0300, Andy Shevchenko wrote:
> >> > > the main issue that driver doesn't
> >> > > send SW_TABLET_MODE event through input device.
> >> >
> >> > Well. Yes. That is one part. If SW_TABLET_MODE is done in the driver, much
> >> > better. My patch was simply in line with some of the other drivers (hp-wmi
> >> > and
> >> > thinkpad_acpi) to get it working for Lenovo Yoga series.
> >>
> >> sysfs ABI for drivers that provide input interface is quite strong for
> >> my opinion. It means I'm not totally objecting, but I would accept it
> >> if and only if there is nothing else could be done.
> >
> > The need we have in the user application is for read-only access.
> 
> I does not matter at all! You are proposing a part of ABI which will
> be closer to what is "carved in stone". Here is the problem.
> 
> So, I'm really trying hard to get avoid such "small things" which
> would make our lives quite hard in long term prospective while fixing
> short-term issues in a good will.
> 
> Please, consider to do it better. For now I didn't hear any proof that
> there is no other way to achieve your goal.

I spent a day with the Lenovo Yoga 2 11 I have available, and have not yet found
a reliable means of detecting the tablet mode (reverse engineering these things
isn't something I'm expert at though). I've reached out to the original author
for some context, but that didn't lead to any revelations as of yet.

Ultimately, this sysfs attribute is no better or worse than others that exist in
our tree. So until we can provide a better solution, we do need to be careful
to not inadvertently favor one laptop driver over another while seeking to avoid
sysfs stable API issues.

I do think we need to start distinguishing between core kernel userspace
interfaces and leaf node driver sysfs attributes.

-- 
Darren Hart
VMware Open Source Technology Center