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

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Message-Id: <fe67c7d0-1671-4bc4-af9f-7207d1f1a18e@www.fastmail.com>
Date:   Thu, 07 Nov 2019 18:06:21 +0900
From:   Blaž Hrastnik <blaz@...n.io>
To:     "Benjamin Tissoires" <benjamin.tissoires@...hat.com>
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.

I've submitted a test containing the Surface Book 2 descriptor.

https://gitlab.freedesktop.org/libevdev/hid-tools/merge_requests/59

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
> >
> 
>