Re: [PATCH v2 1/2] Input: add input_set_property()

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi José,

On Thu, Dec 02, 2021 at 12:08:06PM +0100, José Expósito wrote:
> Buttonpads are expected to map the INPUT_PROP_BUTTONPAD property bit
> and the BTN_LEFT key bit.
> 
> As explained in the specification, where a device has a button type
> value of 0 (click-pad) or 1 (pressure-pad) there should not be
> discrete buttons:
> https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touchpad-windows-precision-touchpad-collection#device-capabilities-feature-report
> 
> However, some drivers map the BTN_RIGHT and/or BTN_MIDDLE key bits even
> though the device is a buttonpad and therefore does not have those
> buttons.
> 
> This behavior has forced userspace applications like libinput to
> implement different workarounds and quirks to detect buttonpads and
> offer to the user the right set of features and configuration options.
> For more information:
> https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/726
> 
> In order to avoid this issue add a helper function for drivers to add
> device properties and make sure that the conditions associated with the
> INPUT_PROP_BUTTONPAD property are meet.
> 
> Notice that this change will not affect udev because it does not check
> for buttons. See systemd/src/udev/udev-builtin-input_id.c.
> 
> List of known affected hardware:
> 
>  - Chuwi AeroBook Plus
>  - Chuwi Gemibook
>  - Framework Laptop
>  - GPD Win Max
>  - Huawei MateBook 2020
>  - Prestigio Smartbook 141 C2
>  - Purism Librem 14v1
>  - StarLite Mk II   - AMI firmware
>  - StarLite Mk II   - Coreboot firmware
>  - StarLite Mk III  - AMI firmware
>  - StarLite Mk III  - Coreboot firmware
>  - StarLabTop Mk IV - AMI firmware
>  - StarLabTop Mk IV - Coreboot firmware
>  - StarBook Mk V
> 
> Signed-off-by: José Expósito <jose.exposito89@gmail.com>
> ---
>  drivers/input/input.c | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/input.h |  1 +
>  2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/input/input.c b/drivers/input/input.c
> index ccaeb2426385..f7e23b3b6ae5 100644
> --- a/drivers/input/input.c
> +++ b/drivers/input/input.c
> @@ -2125,6 +2125,41 @@ void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int
>  }
>  EXPORT_SYMBOL(input_set_capability);
>  
> +/**
> + * input_set_property - add a property to the device
> + * @dev: device to add the property to
> + * @property: type of the property (INPUT_PROP_POINTER, INPUT_PROP_DIRECT...)
> + *
> + * In addition to setting up corresponding bit in dev->propbit the function
> + * might add or remove related capabilities.
> + */
> +void input_set_property(struct input_dev *dev, unsigned int property)
> +{
> +	switch (property) {
> +	case INPUT_PROP_POINTER:
> +	case INPUT_PROP_DIRECT:
> +	case INPUT_PROP_SEMI_MT:
> +	case INPUT_PROP_TOPBUTTONPAD:
> +	case INPUT_PROP_POINTING_STICK:
> +	case INPUT_PROP_ACCELEROMETER:
> +		break;
> +
> +	case INPUT_PROP_BUTTONPAD:
> +		input_set_capability(dev, EV_KEY, BTN_LEFT);
> +		__clear_bit(BTN_RIGHT, dev->keybit);
> +		__clear_bit(BTN_MIDDLE, dev->keybit);

I would prefer if we did this when registering input device, not when
setting this property.

> +		break;
> +
> +	default:
> +		pr_err("%s: unknown property %u\n", __func__, property);
> +		dump_stack();
> +		return;
> +	}
> +
> +	__set_bit(property, dev->propbit);
> +}
> +EXPORT_SYMBOL(input_set_property);
> +
>  static unsigned int input_estimate_events_per_packet(struct input_dev *dev)
>  {
>  	int mt_slots;
> diff --git a/include/linux/input.h b/include/linux/input.h
> index 0354b298d874..5f357687da42 100644
> --- a/include/linux/input.h
> +++ b/include/linux/input.h
> @@ -456,6 +456,7 @@ static inline void input_mt_sync(struct input_dev *dev)
>  }
>  
>  void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int code);
> +void input_set_property(struct input_dev *dev, unsigned int property);
>  
>  /**
>   * input_set_events_per_packet - tell handlers about the driver event rate
> -- 
> 2.25.1
> 

Thanks.

-- 
Dmitry