linux-kernel - Re: [PATCH 3/3] Input: Fix incorrectly halved touchpad range on ELAN v3 touchpads

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Message-ID: <87czb37mpb.fsf@mkorpershoek-xps-13-9370.home>
Date:   Fri, 07 Oct 2022 16:06:08 +0200
From:   Mattijs Korpershoek <mkorpershoek@...libre.com>
To:     Eirin Nya <nyanpasu256@...il.com>, linux-input@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Input: Fix incorrectly halved touchpad range on
 ELAN v3 touchpads

On Thu, Sep 29, 2022 at 01:21, Eirin Nya <nyanpasu256@...il.com> wrote:

> On Linux 5.19.10, on my laptop (Dell Inspiron 15R SE 7520) with an Elan
> v3 touchpad (dmesg says "with firmware version 0x450f02"), the reported
> size of my touchpad (in userspace by calling mtdev_configure() and
> libevdev_get_abs_maximum(), in kernel space
> elantech_device_info::x_max/y_max, either way 1470 by 700) is half that
> of the actual touch range (2940 by 1400), and the upper half of my
> touchpad reports negative values. As a result, with the Synaptics or
> libinput X11 driver set to edge scrolling mode, the entire right half of
> my touchpad has x-values past evdev's reported maximum size, and acts as
> a giant scrollbar!
>
> The problem is that elantech_setup_ps2() -> elantech_set_absolute_mode()
> sets up absolute mode and doubles the hardware resolution (doubling the
> hardware's maximum reported x/y coordinates and its response to
> ETP_FW_ID_QUERY), *after* elantech_query_info() fetches the touchpad
> coordinate system size using ETP_FW_ID_QUERY, which gets cached and
> reported to userspace through ioctl(fd, EVIOCGABS(ABS_X/Y), ...). So the
> touchpad size reported to userspace (and used to subtract vertical
> coordinates from) is half the maximum position of actual touches.
>
> This patch splits out a function elantech_query_range_v3() which fetches
> *only* ETP_FW_ID_QUERY (touchpad size), and calls it a second time if
> elantech_set_absolute_mode() enables double-size mode. This means the
> first call is redundant and wasted if a second call occurs, but this
> minimizes the need to restructure the driver.
>
> Link: https://lore.kernel.org/linux-input/CAL57YxZNutUVxBtvbVWKMw-V2kqeVB5kTQ5BFdJmN=mdPq8Q8Q@mail.gmail.com/
>
> Signed-off-by: Eirin Nya <nyanpasu256@...il.com>

This seems like a candidate patch for stable kernels as well.

Maybe consider adding the following in the commit message footer:
Fixes: 28f49616113f ("Input: elantech - add v3 hardware support")

Reviewed-by: Mattijs Korpershoek <mkorpershoek@...libre.com>

> ---
>  drivers/input/mouse/elantech.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
> index 263779c031..a2176f0fd3 100644
> --- a/drivers/input/mouse/elantech.c
> +++ b/drivers/input/mouse/elantech.c
> @@ -1006,6 +1006,9 @@ static void elantech_set_rate_restore_reg_07(struct psmouse *psmouse,
>  		psmouse_err(psmouse, "restoring reg_07 failed\n");
>  }
>  
> +static int elantech_query_range_v3(struct psmouse *psmouse,
> +				   struct elantech_device_info *info);
> +
>  /*
>   * Put the touchpad into absolute mode
>   */
> @@ -1047,6 +1050,14 @@ static int elantech_set_absolute_mode(struct psmouse *psmouse)
>  		if (elantech_write_reg(psmouse, 0x10, etd->reg_10))
>  			rc = -1;
>  
> +		/*
> +		 * If we boost hardware resolution, we have to re-query
> +		 * info->x_max and y_max.
> +		 */
> +		if (etd->info.set_hw_resolution)
> +			if (elantech_query_range_v3(psmouse, &etd->info))
> +				rc = -1;
> +
>  		break;
>  
>  	case 4:
> @@ -1671,6 +1682,20 @@ static int elantech_set_properties(struct elantech_device_info *info)
>  	return 0;
>  }
>  
> +static int elantech_query_range_v3(struct psmouse *psmouse,
> +				   struct elantech_device_info *info)
> +{
> +	unsigned char param[3];
> +
> +	if (info->send_cmd(psmouse, ETP_FW_ID_QUERY, param))
> +		return -EINVAL;
> +
> +	info->x_max = (0x0f & param[0]) << 8 | param[1];
> +	info->y_max = (0xf0 & param[0]) << 4 | param[2];
> +
> +	return 0;
> +}
> +
>  static int elantech_query_info(struct psmouse *psmouse,
>  			       struct elantech_device_info *info)
>  {
> @@ -1826,11 +1851,8 @@ static int elantech_query_info(struct psmouse *psmouse,
>  		break;
>  
>  	case 3:
> -		if (info->send_cmd(psmouse, ETP_FW_ID_QUERY, param))
> +		if (elantech_query_range_v3(psmouse, info))
>  			return -EINVAL;
> -
> -		info->x_max = (0x0f & param[0]) << 8 | param[1];
> -		info->y_max = (0xf0 & param[0]) << 4 | param[2];
>  		break;
>  
>  	case 4:
> -- 
> 2.37.3