HID: surface-hid: Constify lowlevel HID driver

Since commit 52d225346904 ("HID: Make lowlevel driver structs const")
the lowlevel HID drivers are only exposed as const.

Take advantage of this to constify the underlying structure, too.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230130-hid-const-ll-driver-v1-6-3fc282b3b1d0@weissschuh.net
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

HID: surface-hid: Add support for hot-removal

Add support for hot-removal of SSAM HID client devices.

Once a device has been hot-removed, further communication with it should
be avoided as it may fail and time out. While the device will be removed
as soon as we detect hot-removal, communication may still occur during
teardown, especially when unregistering notifiers.

While hot-removal is a surprise event that can happen at any time, try
to avoid communication as much as possible once it has been detected to
prevent timeouts that can slow down device removal and cause issues,
e.g. when quickly re-attaching the device.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20220527023447.2460025-8-luzmaximilian@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

HID: add suspend/resume helpers

There is a lot of duplication of code in the HID low level drivers.
Better have everything in one place so we can eventually extend it
in a generic way.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211202095334.14399-4-benjamin.tissoires@redhat.com

HID: surface-hid: Fix integer endian conversion

We want to convert from 16 bit (unsigned) little endian values contained
in a packed struct to CPU native endian values here, not the other way
around. So replace cpu_to_le16() with get_unaligned_le16(), using the
latter instead of le16_to_cpu() to acknowledge that we are reading from
a packed struct.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: b05ff1002a5c ("HID: Add support for Surface Aggregator Module HID transport")
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

HID: Add support for Surface Aggregator Module HID transport

Add a HID transport driver to support integrated HID devices on newer
Microsoft Surface models (specifically 7th-generation, i.e. Surface
Laptop 3, Surface Book 3, and later).

On those models, the internal keyboard and touchpad (as well as some
other HID devices with currently unknown function) are connected via the
generic HID subsystem (TC=0x15) of the Surface System Aggregator Module
(SSAM). This subsystem provides a generic HID transport layer, support
for which is implemented by this driver.

Co-developed-by: Blaž Hrastnik <blaz@mxxn.io>
Signed-off-by: Blaž Hrastnik <blaz@mxxn.io>
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>