HID: non-overlapping zeroing of extra bits

From my review of the way the unused bits of report are being zeroed,

From my review of the way the unused bits of report are being zeroed, it seems like there must be a bug. Currently, the zeroing is done in hid_output_field and it covers any bits between the last used bit and the end of the byte. But in case of, say, my keyboard, NumLock is mask 0x01 and CapsLock is 0x02. Invoking hid_output_field for NumLock definitely zeroes across CapsLock. The only reason this works is that the fields are sorted by the offset.

It would be more correct and simpler to zero-fill the buffer into which the fields are set.

The patch is tested with an IBM keyboard that is improperly sensitive to out-of-report pad bits, the extra bits are still zeroed and the fields continue to work as expected. It is also tested with good keyboards.

In case, a related bug in RHEL 5 is tracked with Red Hat bug 513934.

Signed-off-by Pete Zaitcev <[email protected]>

drivers/hid/hid-core.c +0 -5

@@ -940,13 +940,8 @@ static void hid_output_field(struct hid_field *field, __u8 *data)
 	unsigned count = field->report_count;
 	unsigned offset = field->report_offset;
 	unsigned size = field->report_size;
-	unsigned bitsused = offset + count * size;
 	unsigned n;
 
-	/* make sure the unused bits in the last byte are zeros */
-	if (count > 0 && size > 0 && (bitsused % 8) != 0)
-		data[(bitsused-1)/8] &= (1 << (bitsused % 8)) - 1;
-
 	for (n = 0; n < count; n++) {
 		if (field->logical_minimum < 0)	/* signed values */
 			implement(data, offset + n * size, size, s32ton(field->value[n], size));