Re: [PATCH v2 2/2] HID: multitouch: Toggle touch surface on Elan touchpad on lid event

Dmitry Torokhov
2025-11-18T07:12:04Z

On Wed, Nov 12, 2025 at 05:49:53PM -0600, Jonathan Denose wrote:
> Hi Dmitry,
>
> Thanks for your review.
>
> On Tue, Nov 11, 2025 at 4:37 PM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >
> > Hi Jonathan,
> >
> > On Tue, Nov 11, 2025 at 09:34:07PM +0000, Jonathan Denose wrote:
> > > Many touchpad modules have a pin which is expected to be connected to the
> > > lid angle sensor in laptops. The pin sends a signal to the touchpad module
> > > about the lid state and each touchpad vendor handles this notification in
> > > their firmware.
> > >
> > > The Elan touchpad with VID 323b does not always have this aforementioned
> > > pin, which then causes interference between the lid and the touchpad when
> > > the lid is closed. This interference causes a few seconds delay before the
> > > touchpad works again, or it causes it to be come completely unresponsive.
> > > To circumvent this hardware issue in software, implement a device quirk
> > > which will allow the hid-multitouch driver to register a notifier_block
> > > to listen for lid switch events. When the lid switch closes, the
> > > touchpad surface will be turned off and when the lid switch opens, the
> > > touchpad surgace will be turned on. This triggers recalibration which
> > > resolves interference issues when the lid is closed.
> > >
> > > Signed-off-by: Jonathan Denose <jdenose@google.com>
> > > ---
> > > drivers/hid/hid-multitouch.c | 32 +++++++++++++++++++++++++++++++-
> > > 1 file changed, 31 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> > > index 2879e65cf303b1456311ac06115adda5a78a2600..9a89913c193bc110a0a821a901aebd97892c66bd 100644
> > > --- a/drivers/hid/hid-multitouch.c
> > > +++ b/drivers/hid/hid-multitouch.c
> > > @@ -35,6 +35,7 @@
> > > #include <linux/device.h>
> > > #include <linux/hid.h>
> > > #include <linux/module.h>
> > > +#include <linux/notifier.h>
> > > #include <linux/slab.h>
> > > #include <linux/input/mt.h>
> > > #include <linux/jiffies.h>
> > > @@ -76,6 +77,7 @@ MODULE_LICENSE("GPL");
> > > #define MT_QUIRK_DISABLE_WAKEUP BIT(21)
> > > #define MT_QUIRK_ORIENTATION_INVERT BIT(22)
> > > #define MT_QUIRK_APPLE_TOUCHBAR BIT(23)
> > > +#define MT_QUIRK_REGISTER_LID_NOTIFIER BIT(24)
> > >
> > > #define MT_INPUTMODE_TOUCHSCREEN 0x02
> > > #define MT_INPUTMODE_TOUCHPAD 0x03
> > > @@ -183,6 +185,8 @@ struct mt_device {
> > > struct list_head reports;
> > > };
> > >
> > > +static struct hid_device *lid_notify_hdev;
> >
> > This should really be per-device.
>
> Just to be sure I'm following correctly, the initialization of
> lid_notify_hdev should be per-device?

Yes. I believe this is the best practice.

Thanks.

--
Dmitry