Hi,
I've been seeing the following warning when a mode is attempted to be set after boot when no display connectors are connected. This typically happens if your platform has just a HDMI output, and the TV connected to the HDMI output is fully powered off.
This has been happening for quite some time now... I should've probably reported it earlier. I've seen it both with imx-drm and armada-drm.
WARNING: CPU: 0 PID: 846 at drivers/gpu/drm/drm_crtc.c:2074 drm_mode_set_config_internal+0xd0/0xd8() Modules linked in: rfcomm bnep bluetooth 6lowpan_iphc brcmfmac brcmutil snd_soc_fsl_spdif imx_pcm_dma imx_sdma imx_thermal imx2_wdt snd_soc_imx_spdif nfsd exportfs CPU: 0 PID: 846 Comm: Xorg Not tainted 3.14.0+ #1027 Backtrace: [<c0011cf4>] (dump_backtrace) from [<c0011e94>] (show_stack+0x18/0x1c) r6:0000081a r5:00000009 r4:00000000 r3:00000000 [<c0011e7c>] (show_stack) from [<c066b4e8>] (dump_stack+0x74/0x90) [<c066b474>] (dump_stack) from [<c0024588>] (warn_slowpath_common+0x70/0x90) r4:00000000 r3:c09344b8 [<c0024518>] (warn_slowpath_common) from [<c00245cc>] (warn_slowpath_null+0x24/0x2c) r8:ea3c3818 r7:00000001 r6:e9904500 r5:00000000 r4:ea3c3818 [<c00245a8>] (warn_slowpath_null) from [<c03474e4>] (drm_mode_set_config_internal+0xd0/0xd8) [<c0347414>] (drm_mode_set_config_internal) from [<c03497c8>] (drm_mode_setcrtc+0x378/0x4b4) r6:ea3c3400 r5:e8d78b00 r4:e9981e48 r3:00000000 [<c0349450>] (drm_mode_setcrtc) from [<c033c9d0>] (drm_ioctl+0x3f4/0x498) r10:c06b8fa0 r9:e9981e48 r8:e9981e48 r7:e9980000 r6:e98260c0 r5:000000a2 r4:ea3c3400 [<c033c5dc>] (drm_ioctl) from [<c01095b8>] (do_vfs_ioctl+0x80/0x5d4) r10:00000000 r9:e9980000 r8:00000006 r7:c06864a2 r6:be911850 r5:e9826900 r4:ea3bf100 [<c0109538>] (do_vfs_ioctl) from [<c0109b4c>] (SyS_ioctl+0x40/0x5c) r9:e9980000 r8:00000006 r7:c06864a2 r6:be911850 r5:e9826900 r4:e9826900 [<c0109b0c>] (SyS_ioctl) from [<c000e6e0>] (ret_fast_syscall+0x0/0x30) r8:c000e864 r7:00000036 r6:00000006 r5:c06864a2 r4:be911850 r3:00000001 ---[ end trace 46155b08f61d1185 ]---
In drm_mode_set_config_internal(), this check is done:
fb = set->fb;
ret = crtc->funcs->set_config(set); if (ret == 0) { /* crtc->fb must be updated by ->set_config, enforces this. */ WARN_ON(fb != crtc->fb); }
However, drm_crtc_helper_set_config() does this:
if (!set->mode) set->fb = NULL;
if (set->fb) { ... } else { DRM_DEBUG_KMS("[CRTC:%d] [NOFB]\n", set->crtc->base.id); return drm_crtc_helper_disable(set->crtc); }
which results in a zero return with crtc->fb set to NULL, possibly being different to what set->fb was originally.
I haven't debugged this fully yet as the only side effect is the warning.