linux-kernel - Re: [PATCH 2/3] HID: i2c-hid: Read wMaxInputLength of input report instead of bufsize

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Message-ID: <20150224070522.GE1758@lahna.fi.intel.com>
Date:	Tue, 24 Feb 2015 09:05:22 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:	Jiri Kosina <jkosina@...e.cz>, Mark Rutland <mark.rutland@....com>,
	sb@...abs.hk, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] HID: i2c-hid: Read wMaxInputLength of input report
 instead of bufsize

On Mon, Feb 23, 2015 at 10:26:35AM -0500, Benjamin Tissoires wrote:
> On Feb 23 2015 or thereabouts, Mika Westerberg wrote:
> > Wacom digitizer (WCOM0008) on Lenovo Thinkpad 10 seems to allow reading of
> > subsequent reports (or part of them) if we read more than wMaxInputLength
> > of data at the time. This data is not always aligned so that the next
> > report would start right after another.
> > 
> > For example we might get following sequence:
> > 
> >  i2c_hid i2c-WCOM0008:00: input: 0a 00 02 21 20 17 ad 22 11 03
> >  i2c_hid i2c-WCOM0008:00: input: ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03 0a 00 02 21 20 17
> >                                  ad 22 11 03
> >  i2c_hid i2c-WCOM0008:00: input: 02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17 ad 22 11 03 0a 00
> >                                  02 21 20 17
> >  i2c_hid i2c-WCOM0008:00: i2c_hid_get_input: incomplete report (76/8450)
> > 
> > The bufsize is 76 and wMaxInputLength is 10. In above example the first
> > read gets right amount of data. The second and third reads get full bufsize
> > (76 bytes) but the report is missing a start already. This causes the
> > driver to reject the report because we got less than was expected by the
> > report length (0x2102 = 8450).
> > 
> > If we read only wMaxInputLength at the time this does not happen at all and
> > the digitizer works fine.
> > 
> > Based on this change the driver to read wMaxInputLength bytes instead of
> > bufsize if the value looks sane.
> > 
> > Reported-by: Sébastien Bourdeauducq <sb@...abs.hk>
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> 
> We can actually drop this one. Jiri already applied a patch sent last
> week which does the exact same thing:
> https://patchwork.kernel.org/patch/5857521/ (should appear shortly in
> Jiri's tree I guess).

Indeed looks like it does the same. Thanks for letting me know.

> But thanks for confirming that it was really needed for other devices.

No problem :-)
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