Hello Benjamin,

On Wed, 2020-12-02 at 11:21 +0100, Benjamin Tissoires wrote:

Hi Felix,

On Wed, Dec 2, 2020 at 5:31 AM Dmitry Torokhov
[off-list ref] wrote:

quoted

On Thu, Nov 19, 2020 at 12:31 AM Felix Hädicke <
felixhaedicke@web.de> wrote:

quoted

The Apple Magic Trackpad 2 is handled by the magicmouse driver.
And
there were severe stability issues when both drivers (hid-generic
and
hid-magicmouse) were loaded for this device.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=210241

As mentioned in the bug, this hardly looks like the correct solution.

The magicmouse is one of the 2 only drivers that calls
`hid_register_report` and then overwrites the size of the report
manually. I can not figure out immediately if this is wrong, and how
that would impact a free in usbhid, but this is highly suspicious to
me.

Sorry for my late reply.

Now I have now found time to investigate this further, and tried to
understand what effect overwriting the size of the report could have.
Without success, I found nothing about this, which could explain a
memory corruption.

But as I commented in bug 210241 (see comment #13), usbhid_stop() is
called twice for the same hid_device instance pointer. The first call
seems to happen when the HID default driver tries to initialise this
device, which failes (probably because the hid-magicmouse driver is
already active for this device).

Adding the Magic Trackpad 2 to the hid_have_special_driver list makes
hid_generic_match() return false (in the hid-generic driver), and the
device is ignored by this driver.

Is it not the right thing to have the Magic Trackpad 2 in the
hid_have_special_driver list anyway?

Regards,
Felix

Cheers,
Benjamin

quoted

+Jiri Kosina +Benjamin Tissoires for visibility.

quoted

Signed-off-by: Felix Hädicke <redacted>
---
 drivers/hid/hid-quirks.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
index 7a2be0205dfd..0a589d956e5c 100644
--- a/drivers/hid/hid-quirks.c
+++ b/drivers/hid/hid-quirks.c

@@ -473,6 +473,8 @@ static const struct hid_device_id

hid_have_special_driver[] = {
 #if IS_ENABLED(CONFIG_HID_MAGICMOUSE)
        { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_APPLE,
USB_DEVICE_ID_APPLE_MAGICMOUSE) },
        { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_APPLE,
USB_DEVICE_ID_APPLE_MAGICTRACKPAD) },
+       { HID_BLUETOOTH_DEVICE(BT_VENDOR_ID_APPLE,
USB_DEVICE_ID_APPLE_MAGICTRACKPAD2) },
+       { HID_USB_DEVICE(USB_VENDOR_ID_APPLE,
USB_DEVICE_ID_APPLE_MAGICTRACKPAD2) },
 #endif
 #if IS_ENABLED(CONFIG_HID_MAYFLASH)
        { HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE,
USB_DEVICE_ID_DRAGONRISE_PS3) },
--
2.29.2

Thanks.

--
Dmitry