spinlock_t should always be used.

  LD      drivers/gpu/drm/i915/built-in.o
  CHECK   drivers/gpu/drm/i915/i915_drv.c
  CC [M]  drivers/gpu/drm/i915/i915_drv.o
  CHECK   drivers/gpu/drm/i915/i915_dma.c
  CC [M]  drivers/gpu/drm/i915/i915_dma.o
  CHECK   drivers/gpu/drm/i915/i915_irq.c
  CC [M]  drivers/gpu/drm/i915/i915_irq.o
  CHECK   drivers/gpu/drm/i915/i915_debugfs.c
drivers/gpu/drm/i915/i915_debugfs.c:558:31: warning: dereference of noderef expression
drivers/gpu/drm/i915/i915_debugfs.c:558:39: warning: dereference of noderef expression
drivers/gpu/drm/i915/i915_debugfs.c:558:51: warning: dereference of noderef expression
drivers/gpu/drm/i915/i915_debugfs.c:558:63: warning: dereference of noderef expression
  CC [M]  drivers/gpu/drm/i915/i915_debugfs.o
  CHECK   drivers/gpu/drm/i915/i915_suspend.c
  CC [M]  drivers/gpu/drm/i915/i915_suspend.o
  CHECK   drivers/gpu/drm/i915/i915_gem.c
drivers/gpu/drm/i915/i915_gem.c:3703:14: warning: incorrect type in assignment (different base types)
drivers/gpu/drm/i915/i915_gem.c:3703:14:    expected unsigned int [unsigned] [usertype] mask
drivers/gpu/drm/i915/i915_gem.c:3703:14:    got restricted gfp_t
drivers/gpu/drm/i915/i915_gem.c:3706:22: warning: invalid assignment: &=
drivers/gpu/drm/i915/i915_gem.c:3706:22:    left side has type unsigned int
drivers/gpu/drm/i915/i915_gem.c:3706:22:    right side has type restricted gfp_t
drivers/gpu/drm/i915/i915_gem.c:3707:22: warning: invalid assignment: |=
drivers/gpu/drm/i915/i915_gem.c:3707:22:    left side has type unsigned int
drivers/gpu/drm/i915/i915_gem.c:3707:22:    right side has type restricted gfp_t
drivers/gpu/drm/i915/i915_gem.c:3711:39: warning: incorrect type in argument 2 (different base types)
drivers/gpu/drm/i915/i915_gem.c:3711:39:    expected restricted gfp_t [usertype] mask
drivers/gpu/drm/i915/i915_gem.c:3711:39:    got unsigned int [unsigned] [usertype] mask
  CC [M]  drivers/gpu/drm/i915/i915_gem.o
  CHECK   drivers/gpu/drm/i915/i915_gem_context.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_context.o
  CHECK   drivers/gpu/drm/i915/i915_gem_debug.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_debug.o
  CHECK   drivers/gpu/drm/i915/i915_gem_evict.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_evict.o
  CHECK   drivers/gpu/drm/i915/i915_gem_execbuffer.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_execbuffer.o
  CHECK   drivers/gpu/drm/i915/i915_gem_gtt.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_gtt.o
  CHECK   drivers/gpu/drm/i915/i915_gem_stolen.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_stolen.o
  CHECK   drivers/gpu/drm/i915/i915_gem_tiling.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_tiling.o
  CHECK   drivers/gpu/drm/i915/i915_sysfs.c
  CC [M]  drivers/gpu/drm/i915/i915_sysfs.o
  CHECK   drivers/gpu/drm/i915/i915_trace_points.c
  CC [M]  drivers/gpu/drm/i915/i915_trace_points.o
  CHECK   drivers/gpu/drm/i915/intel_display.c
drivers/gpu/drm/i915/intel_display.c:1736:9: warning: mixing different enum types
drivers/gpu/drm/i915/intel_display.c:1736:9:     int enum transcoder  versus
drivers/gpu/drm/i915/intel_display.c:1736:9:     int enum pipe
drivers/gpu/drm/i915/intel_display.c:3659:48: warning: mixing different enum types
drivers/gpu/drm/i915/intel_display.c:3659:48:     int enum pipe  versus
drivers/gpu/drm/i915/intel_display.c:3659:48:     int enum transcoder
  CC [M]  drivers/gpu/drm/i915/intel_display.o
  CHECK   drivers/gpu/drm/i915/intel_crt.c
  CC [M]  drivers/gpu/drm/i915/intel_crt.o
  CHECK   drivers/gpu/drm/i915/intel_lvds.c
  CC [M]  drivers/gpu/drm/i915/intel_lvds.o
  CHECK   drivers/gpu/drm/i915/intel_bios.c
drivers/gpu/drm/i915/intel_bios.c:706:60: warning: incorrect type in initializer (different address spaces)
drivers/gpu/drm/i915/intel_bios.c:706:60:    expected struct vbt_header *vbt
drivers/gpu/drm/i915/intel_bios.c:706:60:    got void [noderef] <asn:2>*vbt
drivers/gpu/drm/i915/intel_bios.c:726:42: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/i915/intel_bios.c:726:42:    expected void const *<noident>
drivers/gpu/drm/i915/intel_bios.c:726:42:    got unsigned char [noderef] [usertype] <asn:2>*
drivers/gpu/drm/i915/intel_bios.c:727:40: warning: cast removes address space of expression
drivers/gpu/drm/i915/intel_bios.c:738:24: warning: cast removes address space of expression
  CC [M]  drivers/gpu/drm/i915/intel_bios.o
  CHECK   drivers/gpu/drm/i915/intel_ddi.c
drivers/gpu/drm/i915/intel_ddi.c:87:6: warning: symbol 'intel_prepare_ddi_buffers' was not declared. Should it be static?
drivers/gpu/drm/i915/intel_ddi.c:1036:34: warning: mixing different enum types
drivers/gpu/drm/i915/intel_ddi.c:1036:34:     int enum pipe  versus
drivers/gpu/drm/i915/intel_ddi.c:1036:34:     int enum transcoder
  CC [M]  drivers/gpu/drm/i915/intel_ddi.o
drivers/gpu/drm/i915/intel_ddi.c: In function ‘intel_ddi_setup_hw_pll_state’:
drivers/gpu/drm/i915/intel_ddi.c:1129:2: warning: ‘port’ may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/gpu/drm/i915/intel_ddi.c:1111:12: note: ‘port’ was declared here
  CHECK   drivers/gpu/drm/i915/intel_dp.c
  CC [M]  drivers/gpu/drm/i915/intel_dp.o
  CHECK   drivers/gpu/drm/i915/intel_hdmi.c
  CC [M]  drivers/gpu/drm/i915/intel_hdmi.o
  CHECK   drivers/gpu/drm/i915/intel_sdvo.c
  CC [M]  drivers/gpu/drm/i915/intel_sdvo.o
  CHECK   drivers/gpu/drm/i915/intel_modes.c
  CC [M]  drivers/gpu/drm/i915/intel_modes.o
  CHECK   drivers/gpu/drm/i915/intel_panel.c
  CC [M]  drivers/gpu/drm/i915/intel_panel.o
  CHECK   drivers/gpu/drm/i915/intel_pm.c
drivers/gpu/drm/i915/intel_pm.c:2173:1: warning: symbol 'mchdev_lock' was not declared. Should it be static?
  CC [M]  drivers/gpu/drm/i915/intel_pm.o
  CHECK   drivers/gpu/drm/i915/intel_i2c.c
  CC [M]  drivers/gpu/drm/i915/intel_i2c.o
  CHECK   drivers/gpu/drm/i915/intel_fb.c
  CC [M]  drivers/gpu/drm/i915/intel_fb.o
  CHECK   drivers/gpu/drm/i915/intel_tv.c
  CC [M]  drivers/gpu/drm/i915/intel_tv.o
  CHECK   drivers/gpu/drm/i915/intel_dvo.c
  CC [M]  drivers/gpu/drm/i915/intel_dvo.o
  CHECK   drivers/gpu/drm/i915/intel_ringbuffer.c
  CC [M]  drivers/gpu/drm/i915/intel_ringbuffer.o
  CHECK   drivers/gpu/drm/i915/intel_overlay.c
  CC [M]  drivers/gpu/drm/i915/intel_overlay.o
  CHECK   drivers/gpu/drm/i915/intel_sprite.c
  CC [M]  drivers/gpu/drm/i915/intel_sprite.o
  CHECK   drivers/gpu/drm/i915/intel_opregion.c
  CC [M]  drivers/gpu/drm/i915/intel_opregion.o
  CHECK   drivers/gpu/drm/i915/dvo_ch7xxx.c
  CC [M]  drivers/gpu/drm/i915/dvo_ch7xxx.o
  CHECK   drivers/gpu/drm/i915/dvo_ch7017.c
  CC [M]  drivers/gpu/drm/i915/dvo_ch7017.o
  CHECK   drivers/gpu/drm/i915/dvo_ivch.c
  CC [M]  drivers/gpu/drm/i915/dvo_ivch.o
  CHECK   drivers/gpu/drm/i915/dvo_tfp410.c
  CC [M]  drivers/gpu/drm/i915/dvo_tfp410.o
  CHECK   drivers/gpu/drm/i915/dvo_sil164.c
  CC [M]  drivers/gpu/drm/i915/dvo_sil164.o
  CHECK   drivers/gpu/drm/i915/dvo_ns2501.c
  CC [M]  drivers/gpu/drm/i915/dvo_ns2501.o
  CHECK   drivers/gpu/drm/i915/i915_gem_dmabuf.c
  CC [M]  drivers/gpu/drm/i915/i915_gem_dmabuf.o
  CHECK   drivers/gpu/drm/i915/i915_ioc32.c
  CC [M]  drivers/gpu/drm/i915/i915_ioc32.o
  CHECK   drivers/gpu/drm/i915/intel_acpi.c
  CC [M]  drivers/gpu/drm/i915/intel_acpi.o
  LD [M]  drivers/gpu/drm/i915/i915.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      drivers/gpu/drm/i915/i915.mod.o
  LD [M]  drivers/gpu/drm/i915/i915.ko

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Reported-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>