On Mar 08 2017 or thereabouts, Tomasz Kramkowski wrote:
> This patch fixes an issue in drivers/hid/hid-input.c where values
> outside of the logical range are not clamped when "null state" bit of
> the input control is not set.
>
> This was discussed on the lists [1] and this change stems from the fact
> due to the ambiguity of the HID specification it might be appropriate to
> follow Microsoft's own interpretation of the specification. As noted in
> Microsoft's documentation [2] in the section titled "Required HID usages
> for digitizers" it is noted that values reported outside the logical
> range "will be considered as invalid data and the value will be changed
> to the nearest boundary value (logical min/max)."
>
> This patch fixes an issue where the (1292:4745) Innomedia INNEX
> GENESIS/ATARI reports out of range values for its X and Y axis of the
> DPad which, due to the null state bit being unset, are forwarded to
> userspace as is. Now these values will get clamped to the logical range
> before being forwarded to userspace. This device was also used to test
> this patch.
>
> This patch expands on commit 3f3752705dbd ("HID: reject input outside
> logical range only if null state is set").
>
> [1]: http://lkml.kernel.org/r/20170307131036.GA853@gaia.local
> [2]: https://msdn.microsoft.com/en-us/library/windows/hardware/dn672278(v=vs.85).asp
>
> Signed-off-by: Tomasz Kramkowski <tk@xxxxxxxxxx>
> ---
> drivers/hid/hid-input.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index cf8256aac2bd..cf38ff79cfe9 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -1157,12 +1157,15 @@ void hidinput_hid_event(struct hid_device *hid, struct hid_field *field, struct
> * don't specify logical min and max.
> */
> if ((field->flags & HID_MAIN_ITEM_VARIABLE) &&
> - (field->flags & HID_MAIN_ITEM_NULL_STATE) &&
> (field->logical_minimum < field->logical_maximum) &&
> (value < field->logical_minimum ||
> value > field->logical_maximum)) {
> - dbg_hid("Ignoring out-of-range value %x\n", value);
> - return;
> + if (field->flags & HID_MAIN_ITEM_NULL_STATE) {
> + dbg_hid("Ignoring out-of-range value %x\n", value);
> + return;
> + }
> + value = value < field->logical_minimum ?
> + field->logical_minimum : field->logical_maximum;
We have a "clamp()" function in the kernel that does the job directly
and which is more readable. Also, this makes testing the out of range
values twice.
How about:
diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index cf8256a..781f400 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1150,19 +1150,26 @@ void hidinput_hid_event(struct hid_device *hid, struct hid_field *field, struct
/*
* Ignore out-of-range values as per HID specification,
- * section 5.10 and 6.2.25.
+ * section 5.10 and 6.2.25, when NULL state bit is present.
+ * When it's not, clamp the value to match Microsoft's input
+ * driver as mentioned in "Required HID usages for digitizers":
+ * https://msdn.microsoft.com/en-us/library/windows/hardware/dn672278(v=vs.85).asp
*
* The logical_minimum < logical_maximum check is done so that we
* don't unintentionally discard values sent by devices which
* don't specify logical min and max.
*/
if ((field->flags & HID_MAIN_ITEM_VARIABLE) &&
- (field->flags & HID_MAIN_ITEM_NULL_STATE) &&
- (field->logical_minimum < field->logical_maximum) &&
- (value < field->logical_minimum ||
- value > field->logical_maximum)) {
- dbg_hid("Ignoring out-of-range value %x\n", value);
- return;
+ (field->logical_minimum < field->logical_maximum)) {
+ if (!(field->flags & HID_MAIN_ITEM_NULL_STATE)) {
+ value = clamp(value,
+ field->logical_minimum,
+ field->logical_maximum);
+ } else if (value < field->logical_minimum ||
+ value > field->logical_maximum) {
+ dbg_hid("Ignoring out-of-range value %x\n", value);
+ return;
+ }
}
/*
---
Cheers,
Benjamin
> }
>
> /*
> --
> 2.12.0
>
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