On Wed, 7 Nov 2012, Benjamin Tissoires wrote:
> HID spec details special values for the HID field unit exponent.
> Basically, the range [0x8..0xf] correspond to [-8..-1], so this is
> a standard two's complement on a half-byte.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoi...@gmail.com>
Acked-by: Jiri Kosina <jkos...@suse.cz>
> ---
> drivers/hid/hid-core.c | 16 +++++++++++++++-
> drivers/hid/hid-input.c | 13 +++++++++----
> include/linux/hid.h | 1 +
> 3 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 3d0da29..9da3007 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -315,6 +315,7 @@ static s32 item_sdata(struct hid_item *item)
>
> static int hid_parser_global(struct hid_parser *parser, struct hid_item
> *item)
> {
> + __u32 raw_value;
> switch (item->tag) {
> case HID_GLOBAL_ITEM_TAG_PUSH:
>
> @@ -365,7 +366,14 @@ static int hid_parser_global(struct hid_parser *parser,
> struct hid_item *item)
> return 0;
>
> case HID_GLOBAL_ITEM_TAG_UNIT_EXPONENT:
> - parser->global.unit_exponent = item_sdata(item);
> + /* Units exponent negative numbers are given through a
> + * two's complement.
> + * See "6.2.2.7 Global Items" for more information. */
> + raw_value = item_udata(item);
> + if (!(raw_value & 0xfffffff0))
> + parser->global.unit_exponent = hid_snto32(raw_value, 4);
> + else
> + parser->global.unit_exponent = raw_value;
> return 0;
>
> case HID_GLOBAL_ITEM_TAG_UNIT:
> @@ -865,6 +873,12 @@ static s32 snto32(__u32 value, unsigned n)
> return value & (1 << (n - 1)) ? value | (-1 << n) : value;
> }
>
> +s32 hid_snto32(__u32 value, unsigned n)
> +{
> + return snto32(value, n);
> +}
> +EXPORT_SYMBOL_GPL(hid_snto32);
> +
> /*
> * Convert a signed 32-bit integer to a signed n-bit integer.
> */
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index 67044f3..7015080 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -192,7 +192,6 @@ static int hidinput_setkeycode(struct input_dev *dev,
> return -EINVAL;
> }
>
> -
> /**
> * hidinput_calc_abs_res - calculate an absolute axis resolution
> * @field: the HID report field to calculate resolution for
> @@ -235,17 +234,23 @@ __s32 hidinput_calc_abs_res(const struct hid_field
> *field, __u16 code)
> case ABS_MT_TOOL_Y:
> case ABS_MT_TOUCH_MAJOR:
> case ABS_MT_TOUCH_MINOR:
> - if (field->unit == 0x11) { /* If centimeters */
> + if (field->unit & 0xffffff00) /* Not a length */
> + return 0;
> + unit_exponent += hid_snto32(field->unit >> 4, 4) - 1;
> + switch (field->unit & 0xf) {
> + case 0x1: /* If centimeters */
> /* Convert to millimeters */
> unit_exponent += 1;
> - } else if (field->unit == 0x13) { /* If inches */
> + break;
> + case 0x3: /* If inches */
> /* Convert to millimeters */
> prev = physical_extents;
> physical_extents *= 254;
> if (physical_extents < prev)
> return 0;
> unit_exponent -= 1;
> - } else {
> + break;
> + default:
> return 0;
> }
> break;
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 9edb06c..a110a3e 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -754,6 +754,7 @@ int hid_connect(struct hid_device *hid, unsigned int
> connect_mask);
> void hid_disconnect(struct hid_device *hid);
> const struct hid_device_id *hid_match_id(struct hid_device *hdev,
> const struct hid_device_id *id);
> +s32 hid_snto32(__u32 value, unsigned n);
>
> /**
> * hid_map_usage - map usage input bits
> --
> 1.7.11.7
>
--
Jiri Kosina
SUSE Labs
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