When intel_update_watermarks is called on skylake from the hw
state readout disable function it calls intel_update_watermarks.
intel_update_watermarks inspects crtc->state, which should be
set to disabled.

This wasn't the case, and this resulted in a divide-by-zero in
skl_update_wm when intel_update_watermarks got called.

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 295 at drivers/gpu/drm/i915/intel_pm.c:2834
skl_update_pipe_wm+0x102/0x8c0 [i915]()
 WARN_ON(!config->num_pipes_active)
 Modules linked in: coretemp i915(+)
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 CPU: 1 PID: 295 Comm: systemd-udevd Tainted: G     U  W       4.5.0-rc4
-xxxxxx #25
 Hardware name: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  0000000000000000 ffff88003777f5a8 ffffffff813485c2 ffff88003777f5f0
  ffffffffa0236240 ffff88003777f5e0 ffffffff81050fce ffff8800aa420000
  ffff8800aba18000 ffff8800aba18000 ffff880037304c00 ffff8800aa420000
 Call Trace:
  [<ffffffff813485c2>] dump_stack+0x67/0x95
  [<ffffffff81050fce>] warn_slowpath_common+0x9e/0xc0
  [<ffffffff8105103c>] warn_slowpath_fmt+0x4c/0x50
  [<ffffffff8106945e>] ? flush_work+0x8e/0x280
  [<ffffffff810693d5>] ? flush_work+0x5/0x280
  [<ffffffffa016add2>] skl_update_pipe_wm+0x102/0x8c0 [i915]
  [<ffffffffa016b96f>] skl_update_wm+0xff/0x5f0 [i915]
  [<ffffffff810928ee>] ? trace_hardirqs_on_caller+0x15e/0x1d0
  [<ffffffff8109296d>] ? trace_hardirqs_on+0xd/0x10
  [<ffffffffa016ce6e>] intel_update_watermarks+0x1e/0x30 [i915]
  [<ffffffffa01d3ee2>] intel_crtc_disable_noatomic+0xd2/0x150 [i915]
  [<ffffffffa01dd3d2>] intel_modeset_setup_hw_state+0xdd2/0xde0 [i915]
  [<ffffffffa01dfd83>] intel_modeset_init+0x15a3/0x1950 [i915]
  [<ffffffffa02160b6>] i915_driver_load+0x13c6/0x1720 [i915]
  [<ffffffff81522160>] ? add_sysfs_fw_map_entry+0x9b/0x9b
  [<ffffffffa00b15ef>] drm_dev_register+0x6f/0xb0 [drm]
  [<ffffffffa00b3b3a>] drm_get_pci_dev+0x10a/0x1d0 [drm]
  [<ffffffffa01582d9>] i915_pci_probe+0x49/0x50 [i915]
  [<ffffffff8138ae30>] pci_device_probe+0x80/0xf0
  [<ffffffff8143e2ac>] driver_probe_device+0x1bc/0x3d0
  [<ffffffff8143e526>] __driver_attach+0x66/0x90
  [<ffffffff8143e4c0>] ? driver_probe_device+0x3d0/0x3d0
  [<ffffffff8143be3b>] bus_for_each_dev+0x5b/0xa0
  [<ffffffff8143db3e>] driver_attach+0x1e/0x20
  [<ffffffff8143d461>] bus_add_driver+0x151/0x270
  [<ffffffff8143eabc>] driver_register+0x8c/0xd0
  [<ffffffff8138a2ed>] __pci_register_driver+0x5d/0x60
  [<ffffffffa00b3c58>] drm_pci_init+0x58/0xf0 [drm]
  [<ffffffff8109296d>] ? trace_hardirqs_on+0xd/0x10
  [<ffffffffa02aa000>] ? 0xffffffffa02aa000
  [<ffffffffa02aa094>] i915_init+0x94/0x9b [i915]
  [<ffffffff81000423>] do_one_initcall+0x113/0x1f0
  [<ffffffff810a4b21>] ? rcu_read_lock_sched_held+0x61/0x90
  [<ffffffff811601dc>] ? kmem_cache_alloc_trace+0x1cc/0x280
  [<ffffffff8111110a>] do_init_module+0x60/0x1c8
  [<ffffffff810c731b>] load_module+0x1ceb/0x2410
  [<ffffffff810c3a60>] ? store_uevent+0x40/0x40
  [<ffffffff811763d1>] ? kernel_read+0x41/0x60
  [<ffffffff810c7c1d>] SYSC_finit_module+0x8d/0xa0
  [<ffffffff810c7c4e>] SyS_finit_module+0xe/0x10
  [<ffffffff815f1e97>] entry_SYSCALL_64_fastpath+0x12/0x6f
 ---[ end trace 1149e9ab3695a423 ]---
 ------------[ cut here ]------------

Changes since v1:
- Clear state before calling any function after .crtc_disable.
Reported-by: NTvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/56D6FD21.7020907@linux.intel.comTested-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NAnder Conselvan de Oliveira <conselvan2@gmail.com>