lkml.org 
[lkml]   [2012]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH v2 02/11] HID: core: fix unit exponent parsing
    From
    Hi Henrik,

    On Mon, Oct 29, 2012 at 8:05 PM, Henrik Rydberg <rydberg@euromail.se> 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@gmail.com>
    >> ---
    >
    > 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


    \
     
     \ /
      Last update: 2012-10-30 11:41    [W:3.102 / U:0.144 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site