Hi -- I've found an issue with HID report descriptor parsing that causes a
field to be generated for what are supposed to be padding bits in the
report. One device that triggers this problem, a Logitech Marble Mouse
trackball, works normally as mouse but causes the /dev/input/eventX
interface to report a bogus axis.
The problem seems to be that when hid-core parses the HID report
descriptor it incorrectly attributes one 'usage' to the 1x6 bit constant
padding item in the MarbleMouse's report and so adds a field for it (see
MarbleMouse report descriptor and the hid-debug device dump below.)
Later on when hid-input prepares the device capabilities for evdev, it
generates BTN_LEFT, BTN_RIGHT, REL_X, REL_Y, and ABS_MISC. The ABS_MISC
is generated from the bogus padding field because the Usage Page is 0
(which is undefined and reserved in USB spec.)
The following change in hid-core.c (kernel 2.4.14) causes the usages for
the padding item to be 0 (and so avoids adding the field for lack of
usages), but I suspect that someone made usages=report_count for a reason.
Usages being recorded differently for arrays vs. variables seems
curious...
hid-core.c:hid_add_field( ... )
{
// ...
if (HID_MAIN_ITEM_VARIABLE & ~flags) { /* ARRAY */
// ...
usages = parser->local.usage_index;
} else { /* VARIABLE */
- usages = parser->global.report_count;
+ usages = parser->local.usage_index;
}
// ...
}
-- Richard Moats ([EMAIL PROTECTED])
-------
Logitech Marble Mouse HID report descriptor:
05 01 Usage Page Generic Desktop
09 02 Usage Mouse
a1 01 Collection Application
05 09 Usage Page Button
19 01 Usage Min Button 1
29 02 Usage Max Button 2
15 00 Logical Min 0
25 01 Logical Max 1
95 02 Report Count 2
75 01 Report Size 1
81 02 Input (Data,Variable,Absolute)
95 01 Report Count 1
75 06 Report Size 6
81 03 Input (Constant,Variable,Absolute)
05 01 Usage Page Generic Desktop
09 01 Usage Pointer
a1 00 Collection Physical
09 30 Usage X
09 31 Usage Y
15 81 Logical Min -127
25 7f Logical Max 127
75 08 Report Size 8
95 02 Report Count 2
81 06 Input (Data,Variable,Relative)
c0 End Collection
c0 End Collection
----------
The hid-debug.c output:
kernel: Manufacturer: Logitech
kernel: Product: USB-PS/2 Trackball
kernel: Application(GenericDesktop.Mouse)
kernel: INPUT[INPUT]
kernel: Field(0)
kernel: Usage(2)
kernel: Button.0001
kernel: Button.0002
kernel: Logical Minimum(0)
kernel: Logical Maximum(1)
kernel: Report Size(1)
kernel: Report Count(2)
kernel: Report Offset(0)
kernel: Flags( Variable Absolute )
kernel: Field(1) <---- field erroneously added
kernel: Usage(1)
kernel: Pointer.0000
kernel: Logical Minimum(0)
kernel: Logical Maximum(1)
kernel: Report Size(6)
kernel: Report Count(1)
kernel: Report Offset(2)
kernel: Flags( Constant Variable Absolute )
kernel: Field(2)
kernel: Physical(GenericDesktop.Pointer)
kernel: Usage(2)
kernel: GenericDesktop.X
kernel: GenericDesktop.Y
kernel: Logical Minimum(-127)
kernel: Logical Maximum(127)
kernel: Report Size(8)
kernel: Report Count(2)
kernel: Report Offset(8)
kernel: Flags( Variable Relative )
_______________________________________________
[EMAIL PROTECTED]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
