[Bug 1942789] Re: On-demand and RTD3 need to be separated

[Dirk Su]

Install Focal on HP EliteOne 800 G6 All-in-One (202008-28167). Enable
focal-proposed channel, install nvidia with "sudo ubuntu-drivers install
nvidia" then reboot system. Check system is in on-demand with "prime-
select query". Since this machine has all-in-one in chassis type, only
enabled off-load mode and disabled RTD3.

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Title:
  On-demand and RTD3 need to be separated

Status in OEM Priority Project:
  Confirmed
Status in nvidia-prime package in Ubuntu:
  Fix Released
Status in nvidia-prime source package in Focal:
  Fix Committed
Status in nvidia-prime source package in Hirsute:
  Won't Fix

Bug description:
  RTD3 is a nvidia GPU feature to support runtime suspend.

  On-demand would be a X offloading feature.

  They are independent, according to discussion on
  https://github.com/tseliot/ubuntu-drivers-common/issues/55.

  Some parts need to be adjusted, e.g.

  ```
      # If we are dealing with NVIDIA PRIME, and runtimepm
      # is supported, enable it
      if (os.path.isfile('/run/nvidia_runtimepm_supported') and
          os.path.isfile('/usr/bin/prime-select')):
          print('Trying to select the on-demand PRIME profile')
          try:
              subprocess.call(['prime-select', 'on-demand'])
          except:
              pass

          # Create the override file for gpu-manager
          with open('/etc/u-d-c-nvidia-runtimepm-override', 'w') as f:
              f.write('# File created by ubuntu-drivers\n')
  ```

  ---

  [Impact]

   * Ubuntu will set GPU mode to performance as default which may use more power
   * User can't use GPU for other purpose (eg: deep-learning) if RTD3 is not supported
   * According to Nvidia README, the RTD3 doesn't support on non-laptop machine

  [Test Plan]

   * Install Ubuntu, and then execute 'ubuntu-drivers install' to install GPU driver. After the installation, reboot the system. Execute "prime-select query" should get "on-demand"
   * Old GPU (which supported by nvidia-390 only) will keep in performance mode, refer LP:1957094. Execute "prime-select query" should get "nvidia"
   * On non-laptop machine. Can set GPU mode to on-demand
   * On laptop with GPU in runtime PM support list. Set GPU mode to on-demand and Nvidia driver is loaded with "NVreg_DynamicPowerManagement=0x02"

  [Where problems could occur]

   * With GPU supported RTD3 not able enable runtime PM on non-laptop.
  But based on the Nvidia README, this case shall not happened.

  [Other Info]

  Changelogs:

  nvidia-prime (0.8.16~0.20.04.2) focal; urgency=medium

    [ Jeremy Szu ]
    * Set on-demand mode as default nvidia mode (LP: #1942307)

    [ Alberto Milone ]
    * prime-select:
      - Detect chassis type and enable RTD3 only
        on laptops (LP: #1942788).
      - on-demand mode doesn't need to depend on
        RTD3 (LP: #1942789).
      - Use bootvga detection when last_gfx_boot
        is not available.
      - Don't check the current profile when setting
        a profile (LP: #1946476).
      - Handle BrokenPipeError (LP: #1965520).

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