vc4: WARNING during suspend to idle of Raspberry Pi 3 Plus

[Stefan Wahren]

Hi,
i'm currently experiment with suspend to idle on the Raspberry Pi [1].

During my tests, i noticed a WARNING of the vc4 during suspend incl.
Runtime PM usage count underflow. It would be nice if someone can look
at it. In case you want to reproduce it, i can prepare a branch with
some improvements/hacks. For example i disabled dwc2/USB because it
cause a lot of trouble during resume.

Here are the steps to trigger this issue:
- make sure necessary kernel options are enabled ( CONFIG_SUSPEND,
CONFIG_PM_DEBUG, CONFIG_PM_ADVANCED_DEBUG )
- make sure no HDMI cable is connected to Raspberry Pi 3 Plus
- Add "no_console_suspend" to cmdline.txt and reboot
- Connect via Debug UART:

echo 1 > /sys/power/pm_debug_messages
echo platform > /sys/power/pm_test
echo freeze > /sys/power/state

Here is the output:

[   75.538497] PM: suspend entry (s2idle)
[   76.915786] Filesystems sync: 1.377 seconds
[   79.678262] rpi_firmware_set_power: Set HDMI to 1
[   79.678634] rpi_firmware_set_power: Set HDMI to 0
[   79.850949] Freezing user space processes
[   79.852460] Freezing user space processes completed (elapsed 0.001
seconds)
[   79.852484] OOM killer disabled.
[   79.852493] Freezing remaining freezable tasks
[   79.853684] Freezing remaining freezable tasks completed (elapsed
0.001 seconds)
[   80.892819] ieee80211 phy0: brcmf_fil_cmd_data: bus is down. we have
nothing to do.
[   80.892843] ieee80211 phy0: brcmf_cfg80211_get_tx_power: error (-5)
[   81.514053] PM: suspend of devices complete after 1659.336 msecs
[   81.514089] PM: start suspend of devices complete after 1660.386 msecs
[   81.515616] PM: late suspend of devices complete after 1.509 msecs
[   81.515938] rpi_firmware_set_power: Set VEC to 0
[   81.516010] rpi_firmware_set_power: Set V3D to 0
[   81.516998] PM: noirq suspend of devices complete after 1.239 msecs
[   81.517016] PM: suspend debug: Waiting for 5 second(s).
[   89.598310] rpi_firmware_set_power: Set V3D to 1
[   90.078228] ------------[ cut here ]------------
[   90.078240] WARNING: CPU: 1 PID: 216 at
drivers/gpu/drm/vc4/vc4_hdmi.c:477
vc4_hdmi_connector_detect_ctx+0x2e4/0x34c [vc4]
[   90.078344] Modules linked in: aes_arm aes_generic cbc crypto_simd
cryptd algif_skcipher af_alg brcmfmac_wcc brcmfmac vc4 brcmutil
snd_soc_hdmi_codec snd_soc_core ac97_bus sha256_generic
snd_pcm_dmaengine libsha256 snd_pcm sha256_arm snd_timer hci_uart
cfg80211 btbcm snd bluetooth soundcore drm_dma_helper crc32_arm_ce
ecdh_generic ecc raspberrypi_hwmon libaes bcm2835_thermal
[   90.078551] CPU: 1 PID: 216 Comm: kworker/1:2 Not tainted 6.9.3-dirty #30
[   90.078568] Hardware name: BCM2835
[   90.078580] Workqueue: events output_poll_execute
[   90.078610] Call trace:
[   90.078624]  unwind_backtrace from show_stack+0x10/0x14
[   90.078660]  show_stack from dump_stack_lvl+0x50/0x64
[   90.078688]  dump_stack_lvl from __warn+0x7c/0x124
[   90.078723]  __warn from warn_slowpath_fmt+0x170/0x178
[   90.078760]  warn_slowpath_fmt from
vc4_hdmi_connector_detect_ctx+0x2e4/0x34c [vc4]
[   90.078862]  vc4_hdmi_connector_detect_ctx [vc4] from
drm_helper_probe_detect_ctx+0x40/0x120
[   90.078951]  drm_helper_probe_detect_ctx from
output_poll_execute+0x160/0x24c
[   90.078982]  output_poll_execute from process_one_work+0x16c/0x3b4
[   90.079012]  process_one_work from worker_thread+0x270/0x488
[   90.079036]  worker_thread from kthread+0xe0/0xfc
[   90.079060]  kthread from ret_from_fork+0x14/0x28
[   90.079080] Exception stack(0xf0af9fb0 to 0xf0af9ff8)
[   90.079096] 9fa0:                                     00000000
00000000 00000000 00000000
[   90.079113] 9fc0: 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000
[   90.079129] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[   90.079141] ---[ end trace 0000000000000000 ]---
[   90.079155] vc4_hdmi 3f902000.hdmi: vc4_hdmi_connector_detect_ctx:
pm_runtime_resume_and_get failed: -13
[   92.638262] rpi_firmware_set_power: Set HDMI to 1
[   95.678251] rpi_firmware_set_power: Set VEC to 1
[   95.678380] PM: noirq resume of devices complete after 9160.930 msecs
[   95.679604] PM: early resume of devices complete after 1.069 msecs
[   95.812230] brcmfmac: brcmf_fw_alloc_request: using
brcm/brcmfmac43455-sdio for chip BCM4345/6
[   95.812282] PM: resume of devices complete after 132.657 msecs
[   95.813246] vc4_hdmi 3f902000.hdmi: Runtime PM usage count underflow!
[   95.814456] OOM killer enabled.
[   95.814466] Restarting tasks ... done.
[   95.817193] random: crng reseeded on system resumption
[   95.819813] rpi_firmware_set_power: Set HDMI to 0
[   95.827808] PM: suspend exit

[1] - https://github.com/raspberrypi/firmware/issues/1894