On Mon, 12 Apr 2010, Pete Zaitcev wrote:
> 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 <zaitcev@xxxxxxxxxx>
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -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));
> @@ -966,6 +961,7 @@ void hid_output_report(struct hid_report *report, __u8 *data)
> if (report->id > 0)
> *data++ = report->id;
>
> + memset(data, 0, ((report->size - 1) >> 3) + 1);
> for (n = 0; n < report->maxfield; n++)
> hid_output_field(report->field[n], data);
> }
I have applied the patch, thanks Pete.
--
Jiri Kosina
SUSE Labs, Novell Inc.
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