linux-kernel - Re: [PATCH 1/2] Input: cros-ec-keyb: Only register keyboard if rows/columns exist

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Message-ID: <CAD=FV=Ux8AmWpsphRL2waUSrp_Vioykn5WTui4UpzsGLr4fdcA@mail.gmail.com>
Date:   Wed, 13 Apr 2022 13:44:12 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, patches@...ts.linux.dev,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        chrome-platform@...ts.linux.dev,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH 1/2] Input: cros-ec-keyb: Only register keyboard if
 rows/columns exist

Hi,

On Tue, Apr 12, 2022 at 8:33 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> If the device is a detachable, we may still probe this device because
> there are some button switches, e.g. volume buttons and power buttons,
> registered by this driver. Let's allow the device node to be missing row
> and column device properties to indicate that the keyboard matrix
> shouldn't be registered. This removes an input device on Trogdor devices
> such as Wormdingler that don't have a matrix keyboard, but still have
> power and volume buttons. That helps userspace understand there isn't
> a keyboard present when the detachable keyboard is disconnected.
>
> Cc: Benson Leung <bleung@...omium.org>
> Cc: Guenter Roeck <groeck@...omium.org>
> Cc: Douglas Anderson <dianders@...omium.org>
> Cc: Hsin-Yi Wang <hsinyi@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>
> I tried to use mkbp info to query the number of rows and columns, but my
> EC firmware doesn't have commit 8505881ed0b9 ("mkbp: Separate MKBP_INFO
> host command from the keyboard driver") so it always returns 8 and 13
> for the rows and columns. Sigh. With updated firmware we could query it,
> or we could rely on DT like we do already.
>
> Originally I was setting the properties to 0, but
> matrix_keypad_parse_properties() spits out an error message in that case
> and so it seems better to delete the properties and check for their
> existence instead. Another alternative would be to change the compatible
> to be "google,cros-ec-keyb-switches" or something that indicates there
> are only switches and no matrix keyboard.
>
>  drivers/input/keyboard/cros_ec_keyb.c | 9 +++++++++
>  1 file changed, 9 insertions(+)

I do wonder if there will be any unintentional side effects here.
Specifically, even though there is truly no keyboard here, I wonder if
anything in the system is relying on the EC to simulate keypresses
even on tablets where the keyboard isn't actually there...

OK, I guess not. While I think it _used_ to be the case that you could
simulate keyboard inputs from the EC console even for devices w/out a
keyboard, it doesn't seem to be the case anymore. I just tried it and
nothing made it through to the AP.

Seems reasonable to me:

Reviewed-by: Douglas Anderson <dianders@...omium.org>