On Wed, 29 Jul 2020, Frank Yang wrote:

The Varmilo VA104M Keyboard (04b4:07b1, reported as Varmilo Z104M)
exposes media control hotkeys as a USB HID consumer control device,
but these keys do not work in the current (5.8-rc1) kernel due to
the incorrect HID report descriptor. Fix the problem by modifying
the internal HID report descriptor.

More specifically, the keyboard report descriptor specifies the
logical boundary as 572~10754 (0x023c ~ 0x2a02) while the usage
boundary is specified as 0~10754 (0x00 ~ 0x2a02). This results in an
incorrect interpretation of input reports, causing inputs to be ignored.
By setting the Logical Minimum to zero, we align the logical boundary
with the Usage ID boundary.

Some notes:

* There seem to be multiple variants of the VA104M keyboard. This
  patch specifically targets 04b4:07b1 variant.

* The device works out-of-the-box on Windows platform with the generic
  consumer control device driver (hidserv.inf). This suggests that
  Windows either ignores the Logical Minimum/Logical Maximum or
  interprets the Usage ID assignment differently from the linux
  implementation; Maybe there are other devices out there that only
  works on Windows due to this problem?

Signed-off-by: Frank Yang <redacted>
---
 drivers/hid/Kconfig       |  6 ++++
 drivers/hid/Makefile      |  1 +
 drivers/hid/hid-ids.h     |  2 ++
 drivers/hid/hid-varmilo.c | 58 +++++++++++++++++++++++++++++++++++++++

Hi Frank,

thanks for the patch.

Given the fact that the device presents itself with CYPRESS VID (0x04b4, 
'officially' assigned to cypress), can we avoid creating extra driver, and 
rather extend hid-cypress.c with this quirk, please?

Thanks,

-- 
Jiri Kosina
SUSE Labs