Hi Henrik,
On Mon, Oct 29, 2012 at 8:05 PM, Henrik Rydberg <rydberg@xxxxxxxxxxx> wrote:
> Hi Benjamin,
>
>> HID spec details special values for the HID field unit exponent.
>> Basically, the range [0x8..0xf] correspond to [-8..-1].
>>
>> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxx>
>> ---
>
> Standard two's complement, in other words?
yes, but for 4-bits values. The thing is that I didn't managed to
figure out if it was allowed to give unit exponent with more than 4
bits...
>
>> drivers/hid/hid-core.c | 10 +++++++++-
>> drivers/hid/hid-input.c | 19 +++++++++++++------
>> 2 files changed, 22 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
>> index 9904776..6bde6e4 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 special
>> + * table.
>> + * See "6.2.2.7 Global Items" for more information. */
>> + raw_value = item_udata(item);
>> + if ((raw_value >> 3) == 1)
>> + parser->global.unit_exponent = raw_value - 16;
>> + else
>> + parser->global.unit_exponent = raw_value;
>
> I beleive the function you want is snto32(value, 4).
but to be sure, we should still do a test against (raw_value & 0xf0)
for values with more than 4 bits, no?
Cheers,
Benjamin
>
>> return 0;
>>
>> case HID_GLOBAL_ITEM_TAG_UNIT:
>> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
>> index 1b0adc3..fc9f2b5 100644
>> --- a/drivers/hid/hid-input.c
>> +++ b/drivers/hid/hid-input.c
>> @@ -215,7 +215,7 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
>> field->logical_minimum;
>> __s32 physical_extents = field->physical_maximum -
>> field->physical_minimum;
>> - __s32 prev;
>> + __s32 prev, tmp_exponent;
>>
>> /* Check if the extents are sane */
>> if (logical_extents <= 0 || physical_extents <= 0)
>> @@ -235,17 +235,24 @@ __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;
>> + tmp_exponent = field->unit >> 4;
>> + if ((tmp_exponent >> 3) == 1)
>> + tmp_exponent -= 16;
>
> Ditto.
>
>> + switch (field->unit & 0xf) {
>> + case 0x1: /* If centimeters */
>> /* Convert to millimeters */
>> - unit_exponent += 1;
>> - } else if (field->unit == 0x13) { /* If inches */
>> + unit_exponent += tmp_exponent;
>> + break;
>> + case 0x3: /* If inches */
>> /* Convert to millimeters */
>> prev = physical_extents;
>> physical_extents *= 254;
>> if (physical_extents < prev)
>> return 0;
>> - unit_exponent -= 1;
>> - } else {
>> + unit_exponent += tmp_exponent - 2;
>> + default:
>> return 0;
>> }
>> break;
>> --
>> 1.7.11.7
>>
>
> Thanks,
> Henrik
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