linux-kernel - Re: [PATCH 1/3] HID: logitech-hidpp: detect HID++ 2.0 errors too

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Message-ID: <4013567.XXXMc2jNn9@al>
Date:	Thu, 18 Dec 2014 18:26:05 +0100
From:	Peter Wu <peter@...ensteyn.nl>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Nestor Lopez Casado <nlopezcasad@...itech.com>,
	linux-input <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] HID: logitech-hidpp: detect HID++ 2.0 errors too

On Tuesday 16 December 2014 09:33:44 Benjamin Tissoires wrote:
> Hi Peter,
> 
> On Mon, Dec 15, 2014 at 7:50 PM, Peter Wu <peter@...ensteyn.nl> wrote:
> > Devices speaking HID++ 2.0 report a different error code (0xff). Detect
> > these errors too to avoid 5 second delays when the device reports an
> > error. Caught by... well, a bug in the QEMU emulation of this receiver.
> >
> > Renamed fap to rap for HID++ 1.0 errors because it is more logical,
> > it has no functional difference.
> >
> > Signed-off-by: Peter Wu <peter@...ensteyn.nl>
> > ---
> 
> I'd like to have Nestor's opinion on this. I did not manage to find on
> the documentation that HID++ 2.0 Long report error code is 0xff, so
> introducing this change without Logitech's blessing would be
> unfortunate.
> I understand this will fix your qemu problem, but I am not entirely
> sure if we do not have to check on 0xff and 0x8f in both short and
> long responses.
> 
> Cheers,
> Benjamin

Hi Benjamin,

The Logitech Unifying extension for Chrome[1] is documented quite well
and contains details which were not public before (including names and
descriptions for all registers and subIDs!).

In lib/devices/HidppFap.js you can find this logic for handling HID++
2.0 messages:

    if ((reqView.getUint8(1) == rspView.getUint8(1)) //  device index
        && (reqView.getUint8(2) == rspView.getUint8(2)) // feature index
        && (reqView.getUint8(3) == rspView.getUint8(3))) // function/event ID + software ID
    {
        result.matchResult = devices.MATCH_RESULT.SUCCESS;
    } else if ((reqView.getUint8(1) == rspView.getUint8(1)) //  device index
        && (0xFF == rspView.getUint8(2)) // Hid++ 2.0 error
        && (reqView.getUint8(2) == rspView.getUint8(3)) // feature index
        && (reqView.getUint8(3) == rspView.getUint8(4))) // function/event ID + software ID
    {
        result.errCode = rspView.getUint8(5); // FAP_ERROR
        result.matchResult = devices.MATCH_RESULT.ERROR;
    }

Looks like a sufficient proof that 0xFF is the correct number to detect
HID++ 2.0 errors right?

In HID++ 1.0 devices ("rap"), 0xFF is named as "SYNC" (with no further
comments), so this will probably not trigger false positives either.

Kind regards,
Peter

 [1]: https://chrome.google.com/webstore/detail/logitech-unifying-for-chr/agpmgihmmmfkbhckmciedmhincdggomo

> >  drivers/hid/hid-logitech-hidpp.c | 17 ++++++++++++++---
> >  1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> > index 2f420c0..ae23dec 100644
> > --- a/drivers/hid/hid-logitech-hidpp.c
> > +++ b/drivers/hid/hid-logitech-hidpp.c
> > @@ -105,6 +105,7 @@ struct hidpp_device {
> >  };
> >
> >
> > +/* HID++ 1.0 error codes */
> >  #define HIDPP_ERROR                            0x8f
> >  #define HIDPP_ERROR_SUCCESS                    0x00
> >  #define HIDPP_ERROR_INVALID_SUBID              0x01
> > @@ -119,6 +120,8 @@ struct hidpp_device {
> >  #define HIDPP_ERROR_REQUEST_UNAVAILABLE                0x0a
> >  #define HIDPP_ERROR_INVALID_PARAM_VALUE                0x0b
> >  #define HIDPP_ERROR_WRONG_PIN_CODE             0x0c
> > +/* HID++ 2.0 error codes */
> > +#define HIDPP20_ERROR                          0xff
> >
> >  static void hidpp_connect_event(struct hidpp_device *hidpp_dev);
> >
> > @@ -192,9 +195,16 @@ static int hidpp_send_message_sync(struct hidpp_device *hidpp,
> >         }
> >
> >         if (response->report_id == REPORT_ID_HIDPP_SHORT &&
> > -           response->fap.feature_index == HIDPP_ERROR) {
> > +           response->rap.sub_id == HIDPP_ERROR) {
> > +               ret = response->rap.params[1];
> > +               dbg_hid("%s:got hidpp error %02X\n", __func__, ret);
> > +               goto exit;
> > +       }
> > +
> > +       if (response->report_id == REPORT_ID_HIDPP_LONG &&
> > +           response->fap.feature_index == HIDPP20_ERROR) {
> >                 ret = response->fap.params[1];
> > -               dbg_hid("__hidpp_send_report got hidpp error %02X\n", ret);
> > +               dbg_hid("%s:got hidpp 2.0 error %02X\n", __func__, ret);
> >                 goto exit;
> >         }
> >
> > @@ -271,7 +281,8 @@ static inline bool hidpp_match_answer(struct hidpp_report *question,
> >  static inline bool hidpp_match_error(struct hidpp_report *question,
> >                 struct hidpp_report *answer)
> >  {
> > -       return (answer->fap.feature_index == HIDPP_ERROR) &&
> > +       return ((answer->rap.sub_id == HIDPP_ERROR) ||
> > +           (answer->fap.feature_index == HIDPP20_ERROR)) &&
> >             (answer->fap.funcindex_clientid == question->fap.feature_index) &&
> >             (answer->fap.params[0] == question->fap.funcindex_clientid);
> >  }
> > --
> > 2.1.3

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