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Date:   Fri, 16 Feb 2018 10:57:22 +0100
From:   Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>
To:     Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, linux-input@vger.kernel.org
Subject: Re: [PATCH 2/3] HID: steam: add serial number information.
Message-ID: <20180216095722.GC18755@casa>
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On Fri, Feb 16, 2018 at 10:31:35AM +0100, Benjamin Tissoires wrote:
> > Ok, I'll do that. The weird thing, however, is that:
> >
> >         hid_hw_raw_request(steam->hid_dev, 0x00,
> >                 buf, hid_report_len(r), /* 64 */
> >                 HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
> >
> > fails with EOVERFLOW. I have to use:
> >
> >         hid_hw_raw_request(steam->hid_dev, 0x00,
> >                 buf, 65
> >                 HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
> >
> > which just feels wrong to me.
> 
> Indeed
> 
> >
> > And looking around drivers/hid/*.c I see that most calls to
> > hid_hw_raw_request(..., HID_REQ_GET_REPORT) use a buffer allocated with
> > {devm_,}kzalloc() and a constant length, never using
> > hid_alloc_report_buf() or hid_report_len().
> 
> well, hid-input.c and hid-multitouch.c are using
> hid_alloc_report_buf() and these two are the most generic ones. We
> haven't converted everybody to use hid_alloc_report_buf(), but it's
> not a reason to not use it for new drivers :)

Agreed. And they use hid_report_len() on the hid_hw_raw_request().

Now my guess is that hid_report_len() should return 65 instead of 64.
And it would do that if the report.id would be >0, but, alas, it is =0.
Maybe feature reports should add 1 without checking id>0? Or maybe
the Steam report descriptor is wrong and I should use report_fixup or
something?

> No, it's unlikely that there is a bug. Can you forward to me the
> report descriptors of the Steam controller (ideally with the tool
> hid-recorder from http://bentiss.github.io/hid-replay-docs/, so I can
> get a few events too)?

Sure, see the attached file. It is the wired one, I opened jstest and
moved the joystick around to get a few events. Unfortunately the
HID_REQ_GET_REPORT are not recorded.

For the casual reader, here is the decoded report descriptor [1]:

0x06, 0x00, 0xFF,  // Usage Page (Vendor Defined 0xFF00)
0x09, 0x01,        // Usage (0x01)
0xA1, 0x01,        // Collection (Application)
0x15, 0x00,        //   Logical Minimum (0)
0x26, 0xFF, 0x00,  //   Logical Maximum (255)
0x75, 0x08,        //   Report Size (8)
0x95, 0x40,        //   Report Count (64)
0x09, 0x01,        //   Usage (0x01)
0x81, 0x02,        //   Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x95, 0x40,        //   Report Count (64)
0x09, 0x01,        //   Usage (0x01)
0x91, 0x02,        //   Output (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
0x95, 0x40,        //   Report Count (64)
0x09, 0x01,        //   Usage (0x01)
0xB1, 0x02,        //   Feature (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
0xC0,              // End Collection


Regards.
Rodrigo

[1]: http://eleccelerator.com/usbdescreqparser/

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Content-Type: text/plain; charset=us-ascii
Content-Description: hid-recorder-steam.txt
Content-Disposition: attachment; filename="steam-hid.txt"

D: 0
R: 33 06 00 ff 09 01 a1 01 15 00 26 ff 00 75 08 95 40 09 01 81 02 95 40 09 01 91 02 95 40 09 01 b1 02 c0
N: Valve Software Wired Controller
P: usb-0000:00:1d.0-1.2/input2
I: 3 28de 1102
D: 0
E: 0.000000 64 01 00 04 0b 06 01 00 00 00 00 00 00 67 14 64 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
E: 1.007977 64 01 00 04 0b 07 01 00 00 00 00 00 00 67 14 64 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
E: 1.087971 64 01 00 01 3c 08 01 00 00 00 00 00 00 00 00 00 00 8b f7 9b 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 3b 02 0c 02 00 00 00 00 67 14
E: 1.095962 64 01 00 01 3c 09 01 00 00 00 00 00 00 00 00 00 00 57 f0 d1 06 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 42 02 17 02 00 00 00 00 67 14
E: 1.103966 64 01 00 01 3c 0a 01 00 00 00 00 00 00 00 00 00 00 11 e5 1e 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 4f 02 22 02 00 00 00 00 67 14
E: 1.115961 64 01 00 01 3c 0b 01 00 00 00 00 00 00 00 00 00 00 4a d7 c5 1a 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 79 01 78 01 5e 02 3a 02 00 00 00 00 67 14
E: 1.123963 64 01 00 01 3c 0c 01 00 00 00 00 00 00 00 00 00 00 40 cb 24 28 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 79 01 78 01 6c 02 4f 02 00 00 00 00 67 14
E: 1.131962 64 01 00 01 3c 0d 01 00 00 00 00 00 00 00 00 00 00 fc be 92 3e 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 7a 02 71 02 00 00 00 00 67 14
E: 1.139954 64 01 00 01 3c 0e 01 00 00 00 00 00 00 00 00 00 00 40 b5 2e 4d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 86 02 86 02 00 00 00 00 67 14
E: 1.151964 64 01 00 01 3c 0f 01 00 00 00 00 00 00 00 00 00 00 3c ac 98 61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 91 02 a3 02 00 00 00 00 67 14
E: 1.159960 64 01 00 01 3c 10 01 00 00 00 00 00 00 00 00 00 00 72 a0 6b 76 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 79 01 79 01 a0 02 c0 02 00 00 00 00 67 14
E: 1.167958 64 01 00 01 3c 11 01 00 00 00 00 00 00 00 00 00 00 26 94 ff 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 b0 02 d8 02 00 00 00 00 67 14
E: 1.175961 64 01 00 01 3c 12 01 00 00 00 00 00 00 00 00 00 00 9d 92 ff 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 b2 02 f8 02 00 00 00 00 67 14
E: 1.239961 64 01 00 01 3c 13 01 00 00 00 00 00 00 00 00 00 00 62 93 ff 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 b1 02 fc 02 00 00 00 00 67 14
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E: 1.267959 64 01 00 01 3c 16 01 00 00 00 00 00 00 00 00 00 00 cb ac ff 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 01 78 01 8f 02 0f 03 00 00 00 00 67 14
E: 1.275960 64 01 00 01 3c 17 01 00 00 00 00 00 00 00 00 00 00 f5 b8 ff 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 79 01 79 01 7e 02 14 03 00 00 00 00 67 14
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