On Wed, 2022-12-07 at 09:58 +0100, Rafael J. Wysocki wrote:

On Tue, Dec 6, 2022 at 3:58 PM Rafael J. Wysocki [off-list ref]
wrote:

quoted

Bastien, Jiri,

Commit 532223c8ac57 ("HID: logitech-hidpp: Enable HID++ for all the
Logitech
Bluetooth devices") caused my Logitech Bluetooth mouse to become
unusable.

Appended is the change I need to make it work again (note that
adding the
device ID to unhandled_hidpp_devices[] doesn't help, so there must
be some
significant enough difference in how the two cases are handled in
the stack).

Here's what I get in the log without the patch below:

[   36.710574] Bluetooth: HIDP (Human Interface Emulation) ver 1.2
[   36.710592] Bluetooth: HIDP socket layer initialized
[   36.724644] hid-generic 0005:046D:B016.0001: unknown main item
tag 0x0
[   36.725860] input: Bluetooth Mouse M336/M337/M535 Mouse as
/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input14
[   36.728036] input: Bluetooth Mouse M336/M337/M535 Consumer
Control as /devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input15
[   36.728823] input: Bluetooth Mouse M336/M337/M535 Keyboard as
/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input18
[   36.731550] hid-generic 0005:046D:B016.0001: input,hidraw0:
BLUETOOTH HID v12.03 Mouse [Bluetooth Mouse M336/M337/M535] on
9c:b6:d0:96:8e:c8
[   36.833039] logitech-hidpp-device 0005:046D:B016.0001: unknown
main item tag 0x0
[   36.999064] logitech-hidpp-device 0005:046D:B016.0001: Device
not connected

and here's what I get with it:

[   43.642546] Bluetooth: HIDP (Human Interface Emulation) ver 1.2
[   43.642559] Bluetooth: HIDP socket layer initialized
[   43.652898] hid-generic 0005:046D:B016.0001: unknown main item
tag 0x0
[   43.653833] input: Bluetooth Mouse M336/M337/M535 Mouse as
/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input14
[   43.655025] input: Bluetooth Mouse M336/M337/M535 Consumer
Control as /devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input15
[   43.655400] input: Bluetooth Mouse M336/M337/M535 Keyboard as
/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-
7:1.0/bluetooth/hci0/hci0:1/0005:046D:B016.0001/input/input18
[   43.657521] hid-generic 0005:046D:B016.0001: input,hidraw0:
BLUETOOTH HID v12.03 Mouse [Bluetooth Mouse M336/M337/M535] on
9c:b6:d0:96:8e:c8

The only difference seems to be that in the former case the
logitech-hidpp
driver tries to bind to the device, but I guess that is expected. 
However,
when the device ID is added to unhandled_hidpp_devices[], the
messages look
exactly like in the "good" case, but the mouse still doesn't work.

Here's what happens.

- The logitech-hidpp driver is modular and is not present initially,
so hid-generic probes first (successfully).

- logitech-hidpp is loaded which causes the device to be reporobed
due
to __hid_bus_driver_added().

- Because the ->match() callback in hid-generic returns 0 for the
device now, it is unbound from the device.

- The probing of logitech-hidpp fails (due to an error in ->probe()).

- The probing of hid-generic fails due to the failing ->match().

So in order for unhandled_hidpp_devices[] in logitech-hidpp to work
with hid-generic, __check_hid_generic() needs to be amended with a
change to run the ->match() callback of the "specific" driver being
tried.

I have a working patch for this that will be sent shortly.

I'm glad my belated questioning of the hid-generic fallback code was
correct ;)

My question about getting the output from the HID++ tool still stands
though.