Re: HID: multitouch: Set to high latency mode on suspend.

["Blaž Hrastnik" <blaz@mxxn.io>]

> Just a couple of quick questions, do you have any reason to implement
> this besides just trying to match the specification?

On the Surface Laptop 3 touchpad and the keyboard are provided by a separate embedded controller that also handles various other components. I think setting the latency mode could improve battery efficiency during suspend. The same should be true for touchpads configured as wake-up sources.

Blaž

On Fri, 15 Jan 2021, at 01:55, Benjamin Tissoires wrote:
> Hi Blaž,
> 
> On Sat, Dec 19, 2020 at 5:55 AM Blaž Hrastnik <blaz@mxxn.io> wrote:
> >
> > Per Windows Precision Touchpad guidelines:
> >
> > > The latency mode feature report is sent by the host to a Windows
> > > Precision Touchpad to indicate when high latency is desirable for
> > > power savings and, conversely, when normal latency is desired for
> > > operation.
> > >
> > > For USB-connected Windows Precision Touchpads, this enables the device
> > > to disambiguate between being suspended for inactivity (runtime IDLE)
> > > and being suspended because the system is entering S3 or Connected
> > > Standby.
> >
> > The current implementation would set the latency to normal on device initialization,
> > but we didn't set the device to high latency on suspend.
> 
> Just a couple of quick questions, do you have any reason to implement
> this besides just trying to match the specification?
> 
> Have you checked if Windows is doing the same thing?
> 
> Cheers,
> Benjamin
> 
> 
> 
> >
> > Signed-off-by: Blaž Hrastnik <blaz@mxxn.io>
> > ---
> >  drivers/hid/hid-multitouch.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> > index d670bcd57..28bac0f39 100644
> > --- a/drivers/hid/hid-multitouch.c
> > +++ b/drivers/hid/hid-multitouch.c
> > @@ -1746,6 +1746,13 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
> >  }
> >
> >  #ifdef CONFIG_PM
> > +static int mt_suspend(struct hid_device *hdev, pm_message_t state)
> > +{
> > +       /* High latency is desirable for power savings during S3/S0ix */
> > +       mt_set_modes(hdev, HID_LATENCY_HIGH, true, true);
> > +       return 0;
> > +}
> > +
> >  static int mt_reset_resume(struct hid_device *hdev)
> >  {
> >         mt_release_contacts(hdev);
> > @@ -1761,6 +1768,8 @@ static int mt_resume(struct hid_device *hdev)
> >
> >         hid_hw_idle(hdev, 0, 0, HID_REQ_SET_IDLE);
> >
> > +       mt_set_modes(hdev, HID_LATENCY_NORMAL, true, true);
> > +
> >         return 0;
> >  }
> >  #endif
> > @@ -2150,6 +2159,7 @@ static struct hid_driver mt_driver = {
> >         .event = mt_event,
> >         .report = mt_report,
> >  #ifdef CONFIG_PM
> > +       .suspend = mt_suspend,
> >         .reset_resume = mt_reset_resume,
> >         .resume = mt_resume,
> >  #endif
> > --
> > 2.29.2
> >
> 
>