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Tue, 07 Apr 2026 21:51:32 -0700 (PDT) Date: Tue, 7 Apr 2026 21:51:30 -0700 From: Dmitry Torokhov To: Thanh Nguyen , Linus Walleij Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Input: zinitix: don't use finger_mask as bitmask when reporting contacts Message-ID: References: <20260408031440.955-1-thanhnguyxn07@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260408031440.955-1-thanhnguyxn07@gmail.com> Hi Thanh, On Tue, Apr 07, 2026 at 10:14:40PM -0500, Thanh Nguyen wrote: > The zinitix touchscreen driver was treating touch_event.finger_mask as a > > bitmask to iterate through finger slots. However, on some devices (e.g., > > Samsung Galaxy A3 2015), finger_mask behaves as a finger count rather than > > a bitmask, causing multitouch to malfunction. > > Instead of relying on finger_mask as a bitmask, iterate through all > > possible finger slots and check if SUB_BIT_EXIST is set for each slot. > > This restores proper multitouch functionality on affected devices. > > Fixes: e941dc13fd (") So this is effectively a revert of e941dc13fd37 ("Input: zinitix - do not report shadow fingers") and Linus reported that on his device ignoring finger count/mask field results in "shadow" contains being reported, so we obviously can not apply this as is. So the question is whether this is a mask or a count? Could it be that it is actually a count of reported slots and we need to stop the loop after we process the "count" number of slots because the rest is simply on-stack garbage? Cc-ing Linus who authored the commit in question... > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=221278 > > Signed-off-by: Thanh Nguyen > --- > drivers/input/touchscreen/zinitix.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/input/touchscreen/zinitix.c b/drivers/input/touchscreen/zinitix.c > index 716d6fa60..b80525443 100644 > --- a/drivers/input/touchscreen/zinitix.c > +++ b/drivers/input/touchscreen/zinitix.c > @@ -445,7 +445,6 @@ static irqreturn_t zinitix_ts_irq_handler(int irq, void *bt541_handler) > struct bt541_ts_data *bt541 = bt541_handler; > struct i2c_client *client = bt541->client; > struct touch_event touch_event; > - unsigned long finger_mask; > __le16 icon_events; > int error; > int i; > @@ -470,11 +469,12 @@ static irqreturn_t zinitix_ts_irq_handler(int irq, void *bt541_handler) > zinitix_report_keys(bt541, le16_to_cpu(icon_events)); > } > > - finger_mask = touch_event.finger_mask; > - for_each_set_bit(i, &finger_mask, MAX_SUPPORTED_FINGER_NUM) { > + /* Process all finger slots and check if they exist, rather than relying on finger_mask as a bitmask. > + * On some devices (e.g., Samsung A3 2015), finger_mask behaves as finger count rather than bitmask. > + * Only process contacts that are actually reported as existing. */ > + for (i = 0; i < MAX_SUPPORTED_FINGER_NUM; i++) { > const struct point_coord *p = &touch_event.point_coord[i]; > > - /* Only process contacts that are actually reported */ > if (p->sub_status & SUB_BIT_EXIST) > zinitix_report_finger(bt541, i, p); > } Thanks. -- Dmitry