drm/i915: WARN_ON_ONCE(!crtc_clock || cdclk < crtc_clock)

[Paul Bolle]

On a laptop that tracks the latest stable release (Ie, it now runs
v4.8.1) I see this WARNING
    WARN_ON_ONCE(!crtc_clock || cdclk < crtc_clock)

Full trace pasted below. I never saw this WARNING before v4.8. Since
v4.8 I've had it in all (four, actually) boots.

What am I expected to do about this WARNING?

Thanks,


Paul Bolle

WARNING: CPU: 3 PID: 1368 at drivers/gpu/drm/i915/intel_display.c:14178 skl_max_scale.part.120+0x75/0x80 [i915]
WARN_ON_ONCE(!crtc_clock || cdclk < crtc_clock)
Modules linked in:
 rfcomm fuse nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_nat nf_conntrack_ipv6 cmac nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_raw iptable_security ebtable_filter ebtables ip6table_filter ip6_tables bnep vfat fat arc4 snd_hda_codec_hdmi snd_soc_skl dell_led snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_hda_ext_core snd_soc_sst_match snd_soc_core intel_rapl snd_hda_codec_realtek snd_hda_codec_generic x86_pkg_temp_thermal coretemp kvm_intel snd_compress snd_pcm_dmaengine ac97_bus kvm snd_hda_intel iwlmvm snd_hda_codec mac80211 iTCO_wdt
 iTCO_vendor_support uvcvideo snd_hda_core snd_hwdep snd_seq irqbypass dell_laptop i2c_designware_platform i2c_designware_core dell_wmi crct10dif_pclmul dell_smbios dcdbas crc32_pclmul snd_seq_device iwlwifi videobuf2_vmalloc videobuf2_memops ghash_clmulni_intel snd_pcm videobuf2_v4l2 videobuf2_core cfg80211 videodev media joydev pcspkr mei_me rtsx_pci_ms memstick snd_timer i2c_i801 i2c_smbus mei snd btusb soundcore shpchp hci_uart btrtl btbcm btqca idma64 btintel bluetooth intel_pch_thermal processor_thermal_device intel_lpss_pci intel_soc_dts_iosf wmi pinctrl_sunrisepoint intel_lpss_acpi rfkill pinctrl_intel intel_lpss int3400_thermal acpi_als int3403_thermal int340x_thermal_zone kfifo_buf acpi_thermal_rel intel_hid industrialio sparse_keymap acpi_pad tpm_tis tpm_tis_core tpm nfsd auth_rpcgss
 nfs_acl lockd grace sunrpc hid_multitouch i915 rtsx_pci_sdmmc mmc_core i2c_algo_bit drm_kms_helper crc32c_intel drm serio_raw nvme rtsx_pci nvme_core i2c_hid video fjes
CPU: 3 PID: 1368 Comm: Xorg Not tainted 4.8.1-1.local1.fc24.x86_64 #1
Hardware name: Dell Inc. XPS 13 9350/09JHRY, BIOS 1.4.4 06/14/2016
 0000000000000286 00000000df2f374c ffffa31528d53910 ffffffffb83e5cfd
 ffffa31528d53960 0000000000000000 ffffa31528d53950 ffffffffb80a7d5b
 00003762c72b3010 ffffa3151e4d8cc0 ffffa31526c23800 ffffa31526e60000
Call Trace:
 [<ffffffffb83e5cfd>] dump_stack+0x63/0x86
 [<ffffffffb80a7d5b>] __warn+0xcb/0xf0
 [<ffffffffb80a7ddf>] warn_slowpath_fmt+0x5f/0x80
 [<ffffffffb83f5247>] ? sort+0x147/0x220
 [<ffffffffc0132754>] ? drm_atomic_helper_normalize_zpos+0x264/0x300 [drm_kms_helper]
 [<ffffffffc01f20e5>] skl_max_scale.part.120+0x75/0x80 [i915]
 [<ffffffffc01f21b6>] intel_check_primary_plane+0xc6/0xe0 [i915]
 [<ffffffffc0132754>] ? drm_atomic_helper_normalize_zpos+0x264/0x300 [drm_kms_helper]
 [<ffffffffc01e33d2>] intel_plane_atomic_check+0x132/0x1f0 [i915]
 [<ffffffffc012f524>] drm_atomic_helper_check_planes+0x84/0x200 [drm_kms_helper]
 [<ffffffffc01fdd07>] intel_atomic_check+0x9a7/0x11a0 [i915]
 [<ffffffffb822c84a>] ? __kmalloc_track_caller+0x17a/0x210
 [<ffffffffc00bbf07>] drm_atomic_check_only+0x187/0x610 [drm]
 [<ffffffffc00bb6c8>] ? drm_atomic_get_crtc_state+0x88/0x100 [drm]
 [<ffffffffc00bc3a7>] drm_atomic_commit+0x17/0x60 [drm]
 [<ffffffffc012e90c>] drm_atomic_helper_update_plane+0xec/0x130 [drm_kms_helper]
 [<ffffffffc00ab16b>] __setplane_internal+0x22b/0x270 [drm]
 [<ffffffffc00ab2e9>] drm_mode_cursor_universal+0x139/0x240 [drm]
 [<ffffffffc00ab46e>] drm_mode_cursor_common+0x7e/0x180 [drm]
 [<ffffffffc00af9de>] drm_mode_cursor2_ioctl+0xe/0x10 [drm]
 [<ffffffffc00a1f0a>] drm_ioctl+0x1da/0x4b0 [drm]
 [<ffffffffc00af9d0>] ? drm_mode_cursor_ioctl+0x70/0x70 [drm]
 [<ffffffffb81161bd>] ? enqueue_hrtimer+0x3d/0x80
 [<ffffffffb8266693>] do_vfs_ioctl+0xa3/0x5e0
 [<ffffffffb86bc151>] ? __sys_recvmsg+0x51/0x90
 [<ffffffffb8266c49>] SyS_ioctl+0x79/0x90
 [<ffffffffb87fc4f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4