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→The lock mechanisms used by Gralloc buffers (non Mozilla-specific)
How gralloc buffer locking works, varies greatly between drivers. While we only directly deal with the gralloc API, which is the same on all Android devices (android::GraphicBuffer::lock and unlock), the precise lock semantics vary between different vendor-specific lock mechanisms, so we need to pay specific attention to them.
* On Android >= 4.2, a standardized fence mechanism is used, that should work uniformly across all drivers. We do not yet support it. B2G does not yet use Android 4.2. These are called sync points and are discussed here [http://source.android.com/devices/graphics.html] and [https://android.googlesource.com/kernel/common/+/android-3.4/Documentation/sync.txt]. They are currently in the staging tree [https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/staging/android/sync.c] and there is a similar non-android linux concept called dma-buf fences being worked on.
* On Qualcomm hardware pre-Android-4.2, a Qualcomm-specific mechanism, named Genlock, is used. We explicitly support it. More on this below.
* On non-Qualcomm, pre-Android-4.2 hardware, other vendor-specific mechanisms are used, which we do not support (see e.g. {{bug|871624}}).
