It's safe to assume cxsr is already disabled when the crtc is off.
This prevents an unclaimed register warning when the required power
wells are not enabled.

[  262.864984] ------------[ cut here ]------------
[  262.865025] WARNING: CPU: 1 PID: 6799 at drivers/gpu/drm/i915/intel_uncore.c:638 __unclaimed_reg_debug+0x68/0x80 [i915]()
[  262.865029] Unclaimed register detected before reading register 0x186500
[  262.865032] Modules linked in: i915 intel_powerclamp
[  262.865057] CPU: 1 PID: 6799 Comm: kms_pipe_crc_ba Tainted: G     U  W       4.4.0-gfxbench+ #1
[  262.865060] Hardware name: DN2820FYK, BIOS FYBYT10H.86A.0038.2014.0717.1455 07/17/2014
[  262.865064]  ffffffffa0338cf8 ffff88007448ba78 ffffffff813df90c ffff88007448bac0
[  262.865071]  ffff88007448bab0 ffffffff810746e1 0000000000186500 0000000000000001
[  262.865077]  0000000000000001 ffff880074420000 0000000000000000 ffff88007448bb10
[  262.865083] Call Trace:
[  262.865092]  [<ffffffff813df90c>] dump_stack+0x4e/0x82
[  262.865098]  [<ffffffff810746e1>] warn_slowpath_common+0x81/0xc0
[  262.865102]  [<ffffffff81074767>] warn_slowpath_fmt+0x47/0x50
[  262.865128]  [<ffffffffa02a07e8>] __unclaimed_reg_debug+0x68/0x80 [i915]
[  262.865154]  [<ffffffffa02a0e4e>] vlv_read32+0x2de/0x370 [i915]
[  262.865173]  [<ffffffffa0256837>] intel_set_memory_cxsr+0x87/0x1a0 [i915]
[  262.865200]  [<ffffffffa02c4cb3>] intel_pre_plane_update+0xb3/0xf0 [i915]
[  262.865228]  [<ffffffffa02c54b5>] intel_atomic_commit+0x3b5/0x17c0 [i915]
[  262.865234]  [<ffffffff8150dc45>] ? drm_atomic_check_only+0x145/0x660
[  262.865239]  [<ffffffff8150d75a>] ? drm_atomic_set_crtc_for_connector+0x6a/0xe0
[  262.865243]  [<ffffffff8150e192>] drm_atomic_commit+0x32/0x50
[  262.865249]  [<ffffffff814eb155>] drm_atomic_helper_set_config+0x75/0xb0
[  262.865253]  [<ffffffff814fd090>] drm_mode_set_config_internal+0x60/0x110
[  262.865258]  [<ffffffff81501e26>] drm_mode_setcrtc+0x186/0x4f0
[  262.865263]  [<ffffffff814f3eed>] drm_ioctl+0x13d/0x590
[  262.865267]  [<ffffffff81501ca0>] ? drm_mode_setplane+0x1b0/0x1b0
[  262.865273]  [<ffffffff811d4c4c>] do_vfs_ioctl+0x2fc/0x550
[  262.865278]  [<ffffffff8118d5ea>] ? vm_munmap+0x4a/0x60
[  262.865283]  [<ffffffff811e06ba>] ? __fget_light+0x6a/0x90
[  262.865287]  [<ffffffff811d4edc>] SyS_ioctl+0x3c/0x70
[  262.865292]  [<ffffffff8179a75b>] entry_SYSCALL_64_fastpath+0x16/0x73
[  262.865296] ---[ end trace 6387a0ad001bb39f ]---

Testcase: kms_flip.basic-flip-vs-wf_vblank
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93698Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1454514805-10595-4-git-send-email-maarten.lankhorst@linux.intel.comReviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>