In the Linux kernel, the following vulnerability has been resolved:

drm/vc4: hdmi: Move packet RAM enable to PM runtime

Audio can be triggered by the HPD handler and start up before video has
been restored, calling vc4_hdmi_write_infoframe() for the audio infoframe.
vc4_hdmi_write_infoframe() needs Packet RAM to be on to store the
infoframe, however, if the video hasn't been enabled,
vc4_hdmi_encoder_post_crtc_enable() hasn't been called and therefore, the
Packet RAM can be disabled by the time vc4_hdmi_write_infoframe() executes,
causing the following splat:

[  201.570266] ------------[ cut here ]------------
[  201.570293] Packet RAM has to be on to store the packet.
[  201.570367] WARNING: drivers/gpu/drm/vc4/vc4_hdmi.c:683 at vc4_hdmi_write_infoframe+0x404/0x494 [vc4], CPU#0: wireplumber/1606
[...]
[  201.658650] Hardware name: Raspberry Pi 4 Model B Rev 1.5 (DT)
[...]
[  201.758499] Call trace:
[  201.760967]  vc4_hdmi_write_infoframe+0x404/0x494 [vc4] (P)
[  201.766607]  vc4_hdmi_write_audio_infoframe+0x1c/0x28 [vc4]
[  201.772247]  write_infoframe+0xbc/0x140 [drm_display_helper]
[  201.777975]  drm_atomic_helper_connector_hdmi_update_audio_infoframe+0x80/0xdc [drm_display_helper]
[  201.787140]  vc4_hdmi_audio_prepare+0x4ac/0x570 [vc4]
[  201.792252]  drm_connector_hdmi_audio_prepare+0x24/0x30 [drm_display_helper]
[  201.799390]  hdmi_codec_prepare+0x100/0x160 [snd_soc_hdmi_codec]
[  201.805471]  snd_soc_pcm_dai_prepare+0xd4/0x100 [snd_soc_core]
[  201.811375]  __soc_pcm_prepare+0x60/0x12c [snd_soc_core]
[  201.816752]  soc_pcm_prepare+0x34/0x58 [snd_soc_core]
[  201.821863]  snd_pcm_do_prepare+0x70/0x8c [snd_pcm]
[  201.826798]  snd_pcm_action_nonatomic+0xe4/0x174 [snd_pcm]
[  201.832350]  snd_pcm_prepare+0xc8/0xd8 [snd_pcm]
[  201.837021]  snd_pcm_common_ioctl+0x458/0x614 [snd_pcm]
[  201.842308]  snd_pcm_ioctl+0x30/0x48 [snd_pcm]
[  201.846802]  __arm64_sys_ioctl+0x88/0xd8
[  201.850769]  invoke_syscall+0x48/0xf4
[  201.854470]  el0_svc_common+0x80/0xd8
[  201.858171]  do_el0_svc+0x1c/0x28
[  201.861520]  el0_svc+0x3c/0xb0
[  201.864605]  el0t_64_sync_handler+0x68/0xdc
[  201.868834]  el0t_64_sync+0x198/0x19c
[  201.872536] ---[ end trace 0000000000000000 ]---

Considering that Packet RAM enable is essentially a power management
configuration, move its enabling/disabling to the Runtime PM hooks.

Note that post_crtc_disable() still stops all infoframes, but keeps Packet
RAM enabled, leaving it to be disabled by runtime suspend.