Commit ff479731 authored by Jason Gerecke's avatar Jason Gerecke Committed by Jiri Kosina
Browse files

HID: wacom: generic: Treat serial number and related fields as unsigned 

The HID descriptors for most Wacom devices oddly declare the serial
number and other related fields as signed integers. When these numbers
are ingested by the HID subsystem, they are automatically sign-extended
into 32-bit integers. We treat the fields as unsigned elsewhere in the
kernel and userspace, however, so this sign-extension causes problems.
In particular, the sign-extended tool ID sent to userspace as ABS_MISC
does not properly match unsigned IDs used by xf86-input-wacom and libwacom.

We introduce a function 'wacom_s32tou' that can undo the automatic sign
extension performed by 'hid_snto32'. We call this function when processing
the serial number and related fields to ensure that we are dealing with
and reporting the unsigned form. We opt to use this method rather than
adding a descriptor fixup in 'wacom_hid_usage_quirk' since it should be
more robust in the face of future devices.

Ref: https://github.com/linuxwacom/input-wacom/issues/134


Fixes: f85c9dc6 ("HID: wacom: generic: Support tool ID and additional tool types")
CC: <stable@vger.kernel.org> # v4.10+
Signed-off-by: default avatarJason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: default avatarAaron Armstrong Skomra <aaron.skomra@wacom.com>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 43b7029f

drivers/hid/wacom.h

+15 −0
Original line number Diff line number Diff line
@@ -202,6 +202,21 @@ static inline void wacom_schedule_work(struct wacom_wac *wacom_wac, 
	}

}



/*

 * Convert a signed 32-bit integer to an unsigned n-bit integer. Undoes

 * the normally-helpful work of 'hid_snto32' for fields that use signed

 * ranges for questionable reasons.

 */

static inline __u32 wacom_s32tou(s32 value, __u8 n)

{

	switch (n) {

	case 8:  return ((__u8)value);

	case 16: return ((__u16)value);

	case 32: return ((__u32)value);

	}

	return value & (1 << (n - 1)) ? value & (~(~0U << n)) : value;

}



extern const struct hid_device_id wacom_ids[];



void wacom_wac_irq(struct wacom_wac *wacom_wac, size_t len);

drivers/hid/wacom_wac.c

+6 −4
Original line number Diff line number Diff line
@@ -2303,7 +2303,7 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field 
	case HID_DG_TOOLSERIALNUMBER:

		if (value) {

			wacom_wac->serial[0] = (wacom_wac->serial[0] & ~0xFFFFFFFFULL);

			wacom_wac->serial[0] |= (__u32)value;

			wacom_wac->serial[0] |= wacom_s32tou(value, field->report_size);

		}

		return;

	case HID_DG_TWIST:
@@ -2319,15 +2319,17 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field 
		return;

	case WACOM_HID_WD_SERIALHI:

		if (value) {

			__u32 raw_value = wacom_s32tou(value, field->report_size);



			wacom_wac->serial[0] = (wacom_wac->serial[0] & 0xFFFFFFFF);

			wacom_wac->serial[0] |= ((__u64)value) << 32;

			wacom_wac->serial[0] |= ((__u64)raw_value) << 32;

			/*

			 * Non-USI EMR devices may contain additional tool type

			 * information here. See WACOM_HID_WD_TOOLTYPE case for

			 * more details.

			 */

			if (value >> 20 == 1) {

				wacom_wac->id[0] |= value & 0xFFFFF;

				wacom_wac->id[0] |= raw_value & 0xFFFFF;

			}

		}

		return;
@@ -2339,7 +2341,7 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field 
		 * bitwise OR so the complete value can be built

		 * up over time :(

		 */

		wacom_wac->id[0] |= value;

		wacom_wac->id[0] |= wacom_s32tou(value, field->report_size);

		return;

	case WACOM_HID_WD_OFFSETLEFT:

		if (features->offset_left && value != features->offset_left)

CRA Git | Maintained and supported by SUSTech CRA and CCSE