linux-kernel - Re: [PATCH v1 2/2] HID: logitech-hidpp: Add Bluetooth Mouse M336/M337/M535 to unhandled_hidpp

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Date:   Wed, 07 Dec 2022 10:59:10 +0100
From:   Bastien Nocera <hadess@...ess.net>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Jiri Kosina <jikos@...nel.org>,
        Filipe Laíns <lains@...eup.net>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>
Subject: Re: [PATCH v1 2/2] HID: logitech-hidpp: Add Bluetooth Mouse
 M336/M337/M535 to unhandled_hidpp_devices[]

On Wed, 2022-12-07 at 10:47 +0100, Rafael J. Wysocki wrote:
> On Wed, Dec 7, 2022 at 10:29 AM Bastien Nocera <hadess@...ess.net>
> wrote:
> > 
> > On Wed, 2022-12-07 at 10:12 +0100, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.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.

This code will start the generic HID stack if the device doesn't
support HID++:
        hidpp->supported_reports = hidpp_validate_device(hdev);

        if (!hidpp->supported_reports) {
                hid_set_drvdata(hdev, NULL);
                devm_kfree(&hdev->dev, hidpp);
                return hid_hw_start(hdev, HID_CONNECT_DEFAULT);
        }

But in your case the device supports HID++ enough to go past that, but
fails to get the HID++ version, which makes the driver think it's not
connected, and just bails.

> 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@...el.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) },
> > >         {}
> > >  };