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HID: input: Create a utility class for counting scroll events 

To avoid code duplication, this class counts high-resolution scroll
movements and emits the legacy low-resolution events when appropriate.
Drivers should be able to create one instance for each scroll wheel that
they need to handle.

Signed-off-by: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Harry Cutts 2018-08-30 14:56:19 -07:00 committed by Jiri Kosina
parent aaf9978c3c
commit 1ff2e1a44e
2 changed files with 73 additions and 0 deletions
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45
drivers/hid/hid-input.c
View File

@ -1826,3 +1826,48 @@ void hidinput_disconnect(struct hid_device *hid)
}
EXPORT_SYMBOL_GPL(hidinput_disconnect);
/**
* hid_scroll_counter_handle_scroll() - Send high- and low-resolution scroll
* events given a high-resolution wheel
* movement.
* @counter: a hid_scroll_counter struct describing the wheel.
* @hi_res_value: the movement of the wheel, in the mouse's high-resolution
* units.
*
* Given a high-resolution movement, this function converts the movement into
* microns and emits high-resolution scroll events for the input device. It also
* uses the multiplier from &struct hid_scroll_counter to emit low-resolution
* scroll events when appropriate for backwards-compatibility with userspace
* input libraries.
*/
void hid_scroll_counter_handle_scroll(struct hid_scroll_counter *counter,
int hi_res_value)
{
int low_res_scroll_amount;
/* Some wheels will rest 7/8ths of a notch from the previous notch
* after slow movement, so we want the threshold for low-res events to
* be in the middle of the notches (e.g. after 4/8ths) as opposed to on
* the notches themselves (8/8ths).
*/
int threshold = counter->resolution_multiplier / 2;
input_report_rel(counter->dev, REL_WHEEL_HI_RES,
hi_res_value * counter->microns_per_hi_res_unit);
counter->remainder += hi_res_value;
if (abs(counter->remainder) >= threshold) {
/* Add (or subtract) 1 because we want to trigger when the wheel
* is half-way to the next notch (i.e. scroll 1 notch after a
* 1/2 notch movement, 2 notches after a 1 1/2 notch movement,
* etc.).
*/
low_res_scroll_amount =
counter->remainder / counter->resolution_multiplier
+ (hi_res_value > 0 ? 1 : -1);
input_report_rel(counter->dev, REL_WHEEL,
low_res_scroll_amount);
counter->remainder -=
low_res_scroll_amount * counter->resolution_multiplier;
}
}
EXPORT_SYMBOL_GPL(hid_scroll_counter_handle_scroll);

28
include/linux/hid.h
View File

@ -1138,6 +1138,34 @@ static inline u32 hid_report_len(struct hid_report *report)
int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
int interrupt);
/**
* struct hid_scroll_counter - Utility class for processing high-resolution
* scroll events.
* @dev: the input device for which events should be reported.
* @microns_per_hi_res_unit: the amount moved by the user's finger for each
* high-resolution unit reported by the mouse, in
* microns.
* @resolution_multiplier: the wheel's resolution in high-resolution mode as a
* multiple of its lower resolution. For example, if
* moving the wheel by one "notch" would result in a
* value of 1 in low-resolution mode but 8 in
* high-resolution, the multiplier is 8.
* @remainder: counts the number of high-resolution units moved since the last
* low-resolution event (REL_WHEEL or REL_HWHEEL) was sent. Should
* only be used by class methods.
*/
struct hid_scroll_counter {
struct input_dev *dev;
int microns_per_hi_res_unit;
int resolution_multiplier;
int remainder;
};
void hid_scroll_counter_handle_scroll(struct hid_scroll_counter *counter,
int hi_res_value);
/* HID quirks API */
unsigned long hid_lookup_quirk(const struct hid_device *hdev);
int hid_quirks_init(char **quirks_param, __u16 bus, int count);