Currently we make the unilateral decision inside
i915_gem_object_pin_to_display() where the VMA should resided (inside
the fence and mappable region or above?). This is not our decision to
make as it impacts on how the display engine can use the resulting
scanout object, and it would rather instruct us where to place the VMA so
that it can enable the features it wants. As such, make the pin flags an
argument to i915_gem_object_pin_to_display() and control them from
intel_pin_and_fence_fb_obj()

Whilst taking control of the mapping for ourselves, start tracking how
we use it to avoid trying to free a fence we never claimed:

<3>[  227.151869] GEM_BUG_ON(vma->fence->pin_count <= 0)
<4>[  227.152064] ------------[ cut here ]------------
<2>[  227.152068] kernel BUG at drivers/gpu/drm/i915/i915_vma.h:391!
<4>[  227.152084] invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
<0>[  227.152092] Dumping ftrace buffer:
<0>[  227.152099]    (ftrace buffer empty)
<4>[  227.152102] Modules linked in: i915 snd_hda_codec_analog snd_hda_codec_generic coretemp snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_pcm lpc_ich e1000e mei_me mei prime_numbers
<4>[  227.152131] CPU: 1 PID: 1587 Comm: kworker/u16:49 Tainted: G     U           4.16.0-rc1-gbab67b2f6177-kasan_7+ #1
<4>[  227.152134] Hardware name: Dell Inc. OptiPlex 755                 /0PU052, BIOS A08 02/19/2008
<4>[  227.152236] Workqueue: events_unbound intel_atomic_commit_work [i915]
<4>[  227.152292] RIP: 0010:intel_unpin_fb_vma+0x23a/0x2a0 [i915]
<4>[  227.152295] RSP: 0018:ffff88005aad7b68 EFLAGS: 00010286
<4>[  227.152300] RAX: 0000000000000026 RBX: ffff88005c359580 RCX: 0000000000000000
<4>[  227.152304] RDX: 0000000000000026 RSI: ffffffff8707d840 RDI: ffffed000b55af63
<4>[  227.152307] RBP: ffff880056817e58 R08: 0000000000000001 R09: 0000000000000000
<4>[  227.152311] R10: ffff88005aad7b88 R11: 0000000000000000 R12: ffff8800568184d0
<4>[  227.152314] R13: ffff880065b5ab08 R14: 0000000000000000 R15: dffffc0000000000
<4>[  227.152318] FS:  0000000000000000(0000) GS:ffff88006ac40000(0000) knlGS:0000000000000000
<4>[  227.152322] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[  227.152325] CR2: 00007f5fb25550a8 CR3: 0000000068c78000 CR4: 00000000000006e0
<4>[  227.152328] Call Trace:
<4>[  227.152385]  intel_cleanup_plane_fb+0x6b/0xd0 [i915]
<4>[  227.152395]  drm_atomic_helper_cleanup_planes+0x166/0x280
<4>[  227.152452]  intel_atomic_commit_tail+0x159d/0x3380 [i915]
<4>[  227.152463]  ? process_one_work+0x66e/0x1460
<4>[  227.152516]  ? skl_update_crtcs+0x9c0/0x9c0 [i915]
<4>[  227.152523]  ? lock_acquire+0x13d/0x390
<4>[  227.152527]  ? lock_acquire+0x13d/0x390
<4>[  227.152534]  process_one_work+0x71a/0x1460
<4>[  227.152540]  ? __schedule+0x815/0x1e20
<4>[  227.152547]  ? pwq_dec_nr_in_flight+0x2b0/0x2b0
<4>[  227.152553]  ? _raw_spin_lock_irq+0xa/0x40
<4>[  227.152559]  worker_thread+0xdf/0xf60
<4>[  227.152569]  ? process_one_work+0x1460/0x1460
<4>[  227.152573]  kthread+0x2cf/0x3c0
<4>[  227.152578]  ? _kthread_create_on_node+0xa0/0xa0
<4>[  227.152583]  ret_from_fork+0x3a/0x50
<4>[  227.152591] Code: c6 00 11 86 c0 48 c7 c7 e0 bd 85 c0 e8 60 e7 a9 c4 0f ff e9 1f fe ff ff 48 c7 c6 40 10 86 c0 48 c7 c7 e0 ca 85 c0 e8 2b 95 bd c4 <0f> 0b 48 89 ef e8 4c 44 e8 c4 e9 ef fd ff ff e8 42 44 e8 c4 e9
<1>[  227.152720] RIP: intel_unpin_fb_vma+0x23a/0x2a0 [i915] RSP: ffff88005aad7b68

v2: i915_vma_pin_fence() is a no-op if a fence isn't required, so check
vma->fence as well.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180220134208.24988-2-chris@chris-wilson.co.uk