According to the ACPI spec 9.1.1 _DSM (Device Specific Method),
intel_hid_dsm_fn_mask, acquired from function index 0, is "a buffer
containing one bit for each function index". When validitaing fn_index,
it should be compared with corresponding bit.

This buffer is usually longer than a byte. Depending on whether
INTEL_HID_DSM_HEBC_V2_FN exist, it could be either
"Buffer (0x02) { 0xFF, 0x01 }" or "Buffer (0x02) { 0xFF, 0x03 }".
Probably it won't grow larger according to the description. On older
platforms, available functions could be fewer or not supported at all,
i.e., "Buffer (One) { 0x00 }".
Signed-off-by: Zhen Gong <zhengong@usc.edu>
Link: https://lore.kernel.org/r/CAJCLVRCyp0ASdWTx-PxsrDC9zFBPw0U2AtPip+_Hpj2r5gUPwA@mail.gmail.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>