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From: "Blaž Hrastnik" <blaz@mxxn.io>
To: "Benjamin Tissoires" <benjamin.tissoires@redhat.com>
Cc: "Jiri Kosina" <jikos@kernel.org>,
	"open list:HID CORE LAYER" <linux-input@vger.kernel.org>
Subject: Re: HID: multitouch: Set to high latency mode on suspend.
Date: Fri, 15 Jan 2021 13:27:26 +0900	[thread overview]
Message-ID: <91a7cedf-ea95-4fc3-8c89-5f8699656399@www.fastmail.com> (raw)
In-Reply-To: <CAO-hwJ+iA2vMMVEukDFGg_L6RPSRVfEhnB71yaTf-yPgkxLLNg@mail.gmail.com>

> 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
> >
> 
>

  reply	other threads:[~2021-01-15  4:31 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-19  4:47 Blaž Hrastnik
2021-01-14 16:55 ` Benjamin Tissoires
2021-01-15  4:27   ` Blaž Hrastnik [this message]
2021-01-26 10:09 ` Jiri Kosina

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