dmesg ci20 tty switch

[  150.790387] ------------[ cut here ]------------
[  150.790416] WARNING: CPU: 1 PID: 471 at drivers/gpu/drm/jz4780/jz4780_crtc.c:416 jz4780_crtc_mode_set+0x1cc/0x1fc()
[  150.790455] Modules linked in: rfcomm bnep hci_uart bluetooth joydev brcmfmac ir_lirc_codec lirc_dev gpio_ir_recv spidev brcmutil fuse
[  150.790469] CPU: 1 PID: 471 Comm: Xorg Tainted: G        W      3.18.3+ #1
[  150.790544] Stack : 00000001 800761ac 00000000 00000004 00000006 00000000 00000000 00000000
	  00000000 00000000 80ac5992 0000003e 000001d7 00000001 809b28e8 8b024310
	  80a3a6a7 8097f038 000001d7 00000001 80ac3594 8b024310 80a51038 8bee2400
	  8bee1db0 80782058 80a40bf4 800315c4 00000003 00000000 80985328 8ab15874
	  8ab15874 80a40000 00000000 00000000 00000000 00000000 00000000 00000000
	  ...
[  150.790546] Call Trace:
[  150.790563] [<8001a5a8>] show_stack+0xc4/0xe0
[  150.790574] [<80783d4c>] dump_stack+0x70/0xbc
[  150.790588] [<80031778>] warn_slowpath_common+0x84/0xb4
[  150.790596] [<8003182c>] warn_slowpath_null+0x18/0x24
[  150.790602] [<8046b59c>] jz4780_crtc_mode_set+0x1cc/0x1fc
[  150.790613] [<8043d1f8>] drm_crtc_helper_set_mode+0x394/0x5bc
[  150.790621] [<8043ded8>] drm_crtc_helper_set_config+0x914/0xaa4
[  150.790629] [<8045852c>] drm_mode_set_config_internal+0x64/0xf8
[  150.790641] [<80445808>] restore_fbdev_mode+0xd8/0x10c
[  150.790649] [<80445864>] drm_fb_helper_restore_fbdev_mode_unlocked+0x28/0x4c
[  150.790657] [<80447afc>] drm_fb_helper_set_par+0x20/0x78
[  150.790668] [<803fd440>] fb_set_var+0x254/0x440
[  150.790674] [<803f7778>] fbcon_blank+0x28c/0x344
[  150.790685] [<8042aa28>] do_unblank_screen+0xb8/0x204
[  150.790699] [<8041fbc8>] complete_change_console+0x6c/0x10c
[  150.790707] [<8042111c>] vt_ioctl+0x14b4/0x1528
[  150.790724] [<80413eec>] tty_ioctl+0x384/0xbe8
[  150.790734] [<80143d54>] do_vfs_ioctl+0x3dc/0x694
[  150.790740] [<80144060>] SyS_ioctl+0x54/0x94
[  150.790751] [<8001eea8>] syscall_common+0x30/0x54

[  150.790758] ---[ end trace 17bb1023989c7ba1 ]---
[  150.790773] [drm:drm_crtc_helper_set_config] *ERROR* failed to set mode on [CRTC:8]