vcsm_lock_cache not implemented for /dev/vcsm-cma

[cratonica]

Describe the bug
Calling vcsm_lock_cache on a system without /dev/vcsm (the legacy driver), which therefore uses /dev/vcsm-cma fails to lock shared CPU/GPU memory and prints out:

usrvcsm: [vcsm_lock_cache]: IMPLEMENT ME

This message originates from https://github.com/raspberrypi/userland/blob/master/host_applications/linux/libs/sm/user-vcsm.c#L1463

To reproduce
Run a program that attempts to make this call using the noted system configuration. I compiled userland at HEAD this morning.

Expected behaviour
It should lock the memory and allow me to access it from the CPU as it does with /dev/vcsm

Actual behaviour
It fails saying it is unimplemented

System
Copy and paste the results of the raspinfo command in to this section. Alternatively, copy and paste a pastebin link, or add answers to the following questions:

• Which model of Raspberry Pi? Pi Zero 2 W

• Which OS and version (cat /etc/rpi-issue)?
  Raspberry Pi reference 2022-01-28
  Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, f01430c9d8f67a4b9719cc00e74a2079d3834d5d, stage4

• Which firmware version (vcgencmd version)?

Jan 20 2022 13:59:16
Copyright (c) 2012 Broadcom
version bd88f66f8952d34e4e0613a85c7a6d3da49e13e2 (clean) (release) (start_x)

• Which kernel version (uname -a)?
  Linux raspberrypi 5.10.92-v7+ #1514 SMP Mon Jan 17 17:36:39 GMT 2022 armv7l GNU/Linux

Logs
If applicable, add the relevant output from dmesg or similar.

Additional context
Add any other relevant context for the problem.

[6by9]

The vcsm-cma kernel driver doesn't support changing the caching mode, hence the comment. IIRC all mappings are uncached.

The simplest answer is to make it call vcsm_lock, and return a fixed result in cache_result.