linux-kernel - Re: [PATCH] HID: Improve Windows Precision Touchpad detection.

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Date:   Mon, 18 Nov 2019 11:04:13 +0100
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Blaž Hrastnik <blaz@...n.io>
Cc:     Jiri Kosina <jikos@...nel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: Improve Windows Precision Touchpad detection.

On Thu, Nov 7, 2019 at 10:07 AM Blaž Hrastnik <blaz@...n.io> wrote:
>
> I've submitted a test containing the Surface Book 2 descriptor.
>
> https://gitlab.freedesktop.org/libevdev/hid-tools/merge_requests/59

Thanks.

Patch is now queued in branch for-5.5/core.

Cheers,
Benjamin

>
> Blaž
>
> On Thu, 7 Nov 2019, at 17:48, Benjamin Tissoires wrote:
> > Hi Blaž,
> >
> > On Wed, Nov 6, 2019 at 12:03 PM Blaž Hrastnik <blaz@...n.io> wrote:
> > >
> > > Per Microsoft spec, usage 0xC5 (page 0xFF) returns a blob containing
> > > data used to verify the touchpad as a Windows Precision Touchpad.
> > >
> > >    0x85, REPORTID_PTPHQA,    //    REPORT_ID (PTPHQA)
> > >     0x09, 0xC5,              //    USAGE (Vendor Usage 0xC5)
> > >     0x15, 0x00,              //    LOGICAL_MINIMUM (0)
> > >     0x26, 0xff, 0x00,        //    LOGICAL_MAXIMUM (0xff)
> > >     0x75, 0x08,              //    REPORT_SIZE (8)
> > >     0x96, 0x00, 0x01,        //    REPORT_COUNT (0x100 (256))
> > >     0xb1, 0x02,              //    FEATURE (Data,Var,Abs)
> > >
> > > However, some devices, namely Microsoft's Surface line of products
> > > instead implement a "segmented device certification report" (usage 0xC6)
> > > which returns the same report, but in smaller chunks.
> > >
> > >     0x06, 0x00, 0xff,        //     USAGE_PAGE (Vendor Defined)
> > >     0x85, REPORTID_PTPHQA,   //     REPORT_ID (PTPHQA)
> > >     0x09, 0xC6,              //     USAGE (Vendor usage for segment #)
> > >     0x25, 0x08,              //     LOGICAL_MAXIMUM (8)
> > >     0x75, 0x08,              //     REPORT_SIZE (8)
> > >     0x95, 0x01,              //     REPORT_COUNT (1)
> > >     0xb1, 0x02,              //     FEATURE (Data,Var,Abs)
> > >     0x09, 0xC7,              //     USAGE (Vendor Usage)
> > >     0x26, 0xff, 0x00,        //     LOGICAL_MAXIMUM (0xff)
> > >     0x95, 0x20,              //     REPORT_COUNT (32)
> > >     0xb1, 0x02,              //     FEATURE (Data,Var,Abs)
> > >
> > > By expanding Win8 touchpad detection to also look for the segmented
> > > report, all Surface touchpads are now properly recognized by
> > > hid-multitouch.
> > >
> > > Signed-off-by: Blaž Hrastnik <blaz@...n.io>
> > > ---
> >
> > This looks good to me.
> > We *could* shorten the ifs and make only one conditional, but I find
> > it this way more readable and future proof.
> >
> > There is just one last step required before we merge this: add a
> > regression test so we ensure we do not break it in the future.
> >
> > It should be merely a matter of sending a MR to
> > https://gitlab.freedesktop.org/libevdev/hid-tools.
> > It should consist in adding the report descriptor in the same way we
> > have
> > https://gitlab.freedesktop.org/libevdev/hid-tools/blob/master/tests/test_multitouch.py#L1656-1658.
> > Then, make sure an unpatched kernel breaks the multitouch test (sudo
> > pytest-3 -k 'multitouch and TestPTP') and that a patched kernel is
> > fixed.
> >
> > Cheers,
> > Benjamin
> >
> > >  drivers/hid/hid-core.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> > > index 63fdbf09b044..2af597cd5d65 100644
> > > --- a/drivers/hid/hid-core.c
> > > +++ b/drivers/hid/hid-core.c
> > > @@ -742,6 +742,10 @@ static void hid_scan_feature_usage(struct hid_parser *parser, u32 usage)
> > >         if (usage == 0xff0000c5 && parser->global.report_count == 256 &&
> > >             parser->global.report_size == 8)
> > >                 parser->scan_flags |= HID_SCAN_FLAG_MT_WIN_8;
> > > +
> > > +       if (usage == 0xff0000c6 && parser->global.report_count == 1 &&
> > > +           parser->global.report_size == 8)
> > > +               parser->scan_flags |= HID_SCAN_FLAG_MT_WIN_8;
> > >  }
> > >
> > >  static void hid_scan_collection(struct hid_parser *parser, unsigned type)
> > > --
> > > 2.23.0
> > >
> >
> >