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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 7 Dec 2022 10:47:17 +0100
Message-ID: <CAJZ5v0ibpzoBLXKiqzciYv1Htks0=4+4_XGLvpH7MCyFoYJiDg@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] HID: logitech-hidpp: Add Bluetooth Mouse
 M336/M337/M535 to unhandled_hidpp_devices[]
To:     Bastien Nocera <hadess@hadess.net>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Jiri Kosina <jikos@kernel.org>,
        =?UTF-8?Q?Filipe_La=C3=ADns?= <lains@riseup.net>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        linux-input@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Thorsten Leemhuis <regressions@leemhuis.info>
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On Wed, Dec 7, 2022 at 10:29 AM Bastien Nocera <hadess@hadess.net> wrote:
>
> On Wed, 2022-12-07 at 10:12 +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Evidently, Logitech Bluetooth Mouse M336/M337/M535 (0xb016) does not
> > work when HID++ is enabled for it,
>
> This needs the output of the hidpp-list-features tool mentioned earlier
> in the thread so we can avoid words like "evidently" and provide
> concrete proof.

Well, so point me to a binary of this, please.

> But why is it needed in this case?

Because it doesn't work otherwise.

> We purposefully try to avoid blanket
> blocklists. The lack of HID++ can be probed, so the device should work
> just as it used to (if the fallback code works).

No, because the hid-generic driver has no way to check that the probe
function of your driver fails for this particular device.  The probing
of hid-generic will fail so long as the device matches the device ID
list of any specific HID driver.  With patch [1/2] from this series
applied this is unless that specific driver has a ->match() callback
rejecting the given device.

You'd need a list of drivers that have been tried and failed somewhere
for that and AFAICS no such list is present in the code.

So a minimum fix for 6.1 that actually works for me is to add the
non-working device to the blocklist.  More sophisticated stuff can be
done later.

> We should only list devices that need special handling, and the ones
> that don't work once HID++ was probed unsuccessfully.
>
> >  so add it to the list of devices
> > that are not handled by logitech-hidpp.
> >
> > Fixes: 532223c8ac57 ("HID: logitech-hidpp: Enable HID++ for all the
> > Logitech Bluetooth devices")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/hid/hid-logitech-hidpp.c |    1 +
> >  1 file changed, 1 insertion(+)
> >
> > Index: linux-pm/drivers/hid/hid-logitech-hidpp.c
> > ===================================================================
> > --- linux-pm.orig/drivers/hid/hid-logitech-hidpp.c
> > +++ linux-pm/drivers/hid/hid-logitech-hidpp.c
> > @@ -4274,6 +4274,7 @@ static const struct hid_device_id unhand
> >         { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_LOGITECH,
> > USB_DEVICE_ID_LOGITECH_HARMONY_PS3) },
> >         /* Handled in hid-generic */
> >         { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_LOGITECH,
> > USB_DEVICE_ID_LOGITECH_DINOVO_EDGE_KBD) },
> > +       { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_LOGITECH, 0xb016) },
> >         {}
> >  };