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The Apple Magic Trackpad 2 (USB-C) reports a wildly wrong battery
capacity over Bluetooth, for example a constant 4% for a pack that is
actually at 74%.
The device's battery input report (0x90) is laid out as
[report-id][status][charge]. hid-input's synchronous capacity query,
hidinput_query_battery_capacity(), assumes the common
[report-id][capacity] layout and returns buf[1], which for this device
is the status byte rather than the charge (buf[2]).
magicmouse_fetch_battery(), which requests the battery report through
hid_hw_request() so the reply is decoded via the report descriptor at
the correct field offset, is gated to the USB models and never runs
over Bluetooth. The device does not push battery reports on its own
either, except a single one at connect time, which is delivered while
probe holds driver_input_lock and is silently dropped. All userspace
reads therefore go through the misparsing query, and the device is
stuck reporting its status byte as the capacity.
Enabling the fetch for Bluetooth is not sufficient on its own: user
space reacts to the power_supply registration immediately, so a query
is typically already in flight when the fetch reply is parsed.
hidinput_get_battery_property() stores the query result and marks the
battery as queried without rechecking whether a report arrived while
it was waiting, clobbering the just-reported correct value with the
misparsed one.
Fix this by adding HID_BATTERY_QUIRK_AVOID_QUERY for the Bluetooth
Magic Trackpad USB-C so the misparsing query path is never used, and
by fetching the battery at the end of probe for this device. hidp has
no asynchronous request() callback, so the fetch is serviced
synchronously via __hid_request() while probe still holds
driver_input_lock; call hid_device_io_start() first so the reply is
processed instead of being discarded.
Tested with a Magic Trackpad USB-C (004c:0324) over Bluetooth on
6.18.37: the reported capacity now matches the device (verified against
a raw GET_REPORT of report 0x90) and updates on reconnect.
Fixes: 87a2f10395 ("HID: magicmouse: Apple Magic Trackpad 2 USB-C driver support")
Cc: stable@vger.kernel.org
Signed-off-by: Andrei Fed <andfed.net@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
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