Re: [PATCH] Input: zinitix: iterate contact slots by finger count

[Nikita Travkin]

Linus Walleij писал(а) 30.06.2026 14:11:
> Hi Thanh,
> 
> sorry for slow reply!
> 
> On Wed, Apr 8, 2026 at 6:19 AM Thanh Nguyen <thanhnguyxn07@xxxxxxxxx> wrote:
>>
>> On affected devices (for example Samsung A3 2015), the value in
>> touch_event.finger_mask appears to behave as a count of reported slots
>> rather than a bitmask. Using for_each_set_bit() can then skip valid
>> contacts and break multitouch gestures.
>>
>> Keep filtering by SUB_BIT_EXIST to avoid reporting shadow contacts, but
>> iterate from slot 0 up to min(finger_mask, MAX_SUPPORTED_FINGER_NUM).
>> This follows the maintainer feedback to treat the field as a possible
>> count while preserving the anti-shadow check.
>>
>> Fixes: e941dc13fd37 ("Input: zinitix - do not report shadow fingers")
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=221278
>> Signed-off-by: Thanh Nguyen <thanhnguyxn07@xxxxxxxxx>
>> ---
>> v2:
>>  - Address maintainer feedback: do not revert e941dc13fd37.
>>  - Keep SUB_BIT_EXIST filtering to avoid shadow contacts.
>>  - Treat finger_mask as a slot-count bound and iterate 0..min(mask, max).
> 
> I can test this if need be, but maybe Nikita want to check it
> first?
> 

Hi!

I've quickly checked it on my gt58 (bt532) but it made me remember that
on this device/chip it seems like only "TOUCH_MODE=0" is supported and
reported fingers don't have extra "width"/"angle" fields. (I have a
vague recollection that this was somehow related to touchkeys being
enabled or not) Otherwise on this chip (firmware? touch_mode?) the
finger count is indeed a count and not a mask. 

Given we have an EXIST bit IMO it still makes sense to make this change.
Maybe also worth adding a short comment why we're treating mask as
count if Linus's devices report mask and your/mine report count...

Nikita

> Yours,
> Linus Walleij