linux-kernel - Re: [PATCH v4 2/2] Input: cros-ec-keyb - Expose function row physical map to userspace

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Message-ID: <161057967168.3661239.10329365279391431594@swboyd.mtv.corp.google.com>
Date:   Wed, 13 Jan 2021 15:14:31 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Philip Chen <philipchen@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        Lee Jones <lee.jones@...aro.org>, linux-input@...r.kernel.org
Subject: Re: [PATCH v4 2/2] Input: cros-ec-keyb - Expose function row physical map to userspace

Quoting Philip Chen (2021-01-13 14:47:18)
> On Tue, Jan 12, 2021 at 10:49 PM Stephen Boyd <swboyd@...omium.org> wrote:
> >
> > Quoting Philip Chen (2021-01-12 15:55:28)
> > > On Mon, Jan 11, 2021 at 6:24 PM Stephen Boyd <swboyd@...omium.org> wrote:
> > > >
> > > > Quoting Philip Chen (2021-01-07 15:42:09)
> > > > > The top-row keys in a keyboard usually have dual functionalities.
> > > > > E.g. A function key "F1" is also an action key "Browser back".
> > > > >
> > > > > Therefore, when an application receives an action key code from
> > > > > a top-row key press, the application needs to know how to correlate
> > > > > the action key code with the function key code and do the conversion
> > > > > whenever necessary.
> > > > >
> > > > > Since the userpace already knows the key scanlines (row/column)
> > > > > associated with a received key code. Essentially, the userspace only
> > > > > needs a mapping between the key row/column and the matching physical
> > > > > location in the top row.
> > > > >
> > > > > This patch enhances the cros-ec-keyb driver to create such a mapping
> > > > > and expose it to userspace in the form of a function-row-physmap
> > > > > attribute. The attribute would be a space separated ordered list of
> > > > > row/column codes, for the keys in the function row, in a left-to-right
> > > > > order.
> > > > >
> > > > > The attribute will only be present when the device has a custom design
> > > > > for the top-row keys.
> > > >
> > > > Is it documented in Documentation/ABI/?
> > > Not yet.
> > > Is it proper to add the documentation to `testing/sysfs-driver-input-keyboard`?
> >
> > Somewhere in testing is fine. I'm not sure if it is a generic proprty
> > for all keyboards though? What's the path in sysfs?
> I wouldn't say it's generic.
> It is available in the keyboard device node only when the board has a
> custom top-row keyboard design.
> The path in sysfs is something like:
> /sys/class/input/input0/device/function_row_physmap, where input0 is
> cros_ec.

I see that atkbd already has this so at least it would be common to some
sort of keyboard device. I'm not sure where to document it though. I see
that atkbd has a handful of undocumented sysfs attributes so adding all
of those may lead to a common path. At the least it sounds OK to have a
sysfs-driver-input-keyboard file if input folks are OK with it.