Re: [PATCH] HID: Accept Digitizers as input devices

["José Expósito" <jose.exposito89@gmail.com>]

Hi Torge,

Thanks for the patch.

On Thu, Aug 04, 2022 at 05:18:32PM +0200, Torge Matthies wrote:
> Commit f7d8e387d9ae ("HID: uclogic: Switch to Digitizer usage for
> styluses") broke input from my XP-Pen Star G640. This is because the
> "Digitizer" usage is not recognized as a valid usage for input devices.
> 
> This patch changes the IS_INPUT_APPLICATION macro so that the "Digitizer"
> (HID_DG_DIGITIZER) usage is recognized as an input device usage.
> 
> Fixes: f7d8e387d9ae ("HID: uclogic: Switch to Digitizer usage for styluses")
> Signed-off-by: Torge Matthies <openglfreak@googlemail.com>
> ---
> This patch could be risky, because any digitizer devices that were
> previously not treated as input devices are now used for input.
> Alternatively the linked commit could be reverted, but that would
> re-introduce the problem detailed in its commit message.
> 
>  include/linux/hid.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I hesitated about this when I sent the patch you mentioned. In the end,
I didn't include any fix because the digitizer use was tested for 2
years in DIGImend, so I (wrongly) assumed that it was safe enough.

However, my initial thought was to add in uclogic_probe():

 	hdev->quirks |= HID_QUIRK_HIDINPUT_FORCE;
+ 	hdev->quirks |= HID_QUIRK_HIDINPUT_FORCE;

Let's see if we can hear more opinions, but if you are worried about
affecting other drivers, that could be a good solution.

Best wishes,
Jose

> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 4363a63b9775..07803e144d98 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -883,7 +883,7 @@ static inline bool hid_is_usb(struct hid_device *hdev)
>  /* We ignore a few input applications that are not widely used */
>  #define IS_INPUT_APPLICATION(a) \
>  		(((a >= HID_UP_GENDESK) && (a <= HID_GD_MULTIAXIS)) \
> -		|| ((a >= HID_DG_PEN) && (a <= HID_DG_WHITEBOARD)) \
> +		|| ((a >= HID_DG_DIGITIZER) && (a <= HID_DG_WHITEBOARD)) \
>  		|| (a == HID_GD_SYSTEM_CONTROL) || (a == HID_CP_CONSUMER_CONTROL) \
>  		|| (a == HID_GD_WIRELESS_RADIO_CTLS))
>  
> -- 
> 2.37.1
>