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

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Message-ID: <YmYZt7WQC17aE1fS@google.com>
Date:   Sun, 24 Apr 2022 20:47:03 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        linux-input@...r.kernel.org, chrome-platform@...ts.linux.dev,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Douglas Anderson <dianders@...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 Stephen,

On Tue, Apr 12, 2022 at 08:33:33PM -0700, Stephen Boyd 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(+)
> 
> diff --git a/drivers/input/keyboard/cros_ec_keyb.c b/drivers/input/keyboard/cros_ec_keyb.c
> index 6534dfca60b4..ac9a953bff02 100644
> --- a/drivers/input/keyboard/cros_ec_keyb.c
> +++ b/drivers/input/keyboard/cros_ec_keyb.c
> @@ -537,6 +537,15 @@ static int cros_ec_keyb_register_matrix(struct cros_ec_keyb *ckdev)
>  	u32 key_pos;
>  	unsigned int row, col, scancode, n_physmap;
>  
> +	/*
> +	 * No rows and columns? There isn't a matrix but maybe there are
> +	 * switches to register in cros_ec_keyb_register_bs() because this is a
> +	 * detachable device.
> +	 */
> +	if (!device_property_read_bool(dev, "keypad,num-rows") &&
> +	    !device_property_read_bool(dev, "keypad,num-cols"))

Why are we abusing device_property_read_bool() for properties that are
not flags instead of using device_property_present()?

> +		return 0;
> +
>  	err = matrix_keypad_parse_properties(dev, &ckdev->rows, &ckdev->cols);
>  	if (err)
>  		return err;
> -- 
> https://chromeos.dev
> 

Thanks.

-- 
Dmitry