ozone: Allocate scanout buffer according to KMS modifiers

ui/ozone/platform/drm/gpu/drm_thread.cc

Index: ui/ozone/platform/drm/gpu/drm_thread.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_thread.cc b/ui/ozone/platform/drm/gpu/drm_thread.cc
index c54e992f66126c9d7d6c130b619c5c10ea0b3cba..c1ea0b1ec1ac7f28fe830d91d16036492ace6155 100644
--- a/ui/ozone/platform/drm/gpu/drm_thread.cc
+++ b/ui/ozone/platform/drm/gpu/drm_thread.cc
@@ -124,8 +124,24 @@ void DrmThread::CreateBuffer(gfx::AcceleratedWidget widget,
       break;
   }
 
-  *buffer = GbmBuffer::CreateBuffer(
-      gbm, ui::GetFourCCFormatFromBufferFormat(format), size, flags);
+  DCHECK(screen_manager_);
+  DrmWindow* window = screen_manager_->GetWindow(widget);
+
+  uint32_t fourcc_format = ui::GetFourCCFormatFromBufferFormat(format);
+  uint64_t modifiers[16];

[Daniele Castagna, 2016/12/16 00:27:41]

It'd be nice if this could go away (for a vector maybe).

[hoegsberg1, 2016/12/17 01:10:49]

Acknowledged.

+  uint32_t nmodifiers = 0;

[Daniele Castagna, 2016/12/16 00:27:41]

nit: s/nmodifiers/num_modifiers or modifiers_size

[hoegsberg1, 2016/12/17 01:10:49]

Ack, but it becomes modifers.size(), even better.

+
+  if (window && window->GetController()) {

[Daniele Castagna, 2016/12/16 00:27:41]

Did we figure out when this is not the case?

[hoegsberg1, 2016/12/17 01:10:49]

No... maybe related to the logout button race? (crbug.com/671293)

+    nmodifiers = window->GetController()->GetFormatModifiers(fourcc_format,
+							     modifiers, arraysize(modifiers));
+  }
+
+  if (nmodifiers > 0 && !(flags & GBM_BO_USE_LINEAR))

[Daniele Castagna, 2016/12/16 00:27:41]

Why do we need to special case for GBM_BO_USE_LINEAR?

[hoegsberg1, 2016/12/17 01:10:49]

If we need a linear buffer, we can either 1) go through the regular
gbm_bo_create() and pass the use flag or 2) filter the modifiers and leave only
DRM_FORMAT_MOD_NONE (= linear).  If we don't do anything, we end up allocating
an AFBC buffer.

+    *buffer = GbmBuffer::CreateBufferWithModifiers(

[Daniele Castagna, 2016/12/16 00:27:41]

nit: if you split the body of an if, you need to add brackets.

[hoegsberg1, 2016/12/17 01:10:49]

Acknowledged.

+        gbm, fourcc_format, size, flags, modifiers, nmodifiers);
+  else
+    *buffer = GbmBuffer::CreateBuffer(
+        gbm, fourcc_format, size, flags);
 }
 
 void DrmThread::CreateBufferFromFds(