Freescale Semiconductor i.MX 6SoloLite Linux, Справочное руководство

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• Composite operations for source/target drawables containing at least 640 pixels. If
less than 640 pixels, the composite path falls to software.
• Simple source composite operations are used when source/target drawables contain
more than 1024x1024 pixels (operations with mask not supported).
• Constant source (with or without alpha mask) composite with target.
• Repeating pattern source (with or without alpha mask) composite with target.
• Only these blending functions: SOURCE, OVER, IN, IN-REVERSE, OUT-
REVERSE, and ADD (some of these need to support the accelerated component-
alpha blending).
• In general, the following types of less commonly used EXA composite operations are
not accelerated:
• Transformed (meaning scaled, rotated) sources and masks.
• Gradient sources.
• Alpha masks with repeating patterns.
The implementation handles all pixmap allocation for X through the EXA callback
interface. A first attempt is made to allocate the memory where it can be accessed by a
physical GPU address. This attempt may fail if there is insufficient GPU accessible
memory remaining, but it can also fail when the bits per pixel, which are being requested
for the pixmap, are less than 8. If the attempt to allocate from the GPU accessible
memory fails, the memory is allocated from the system. If the pixmap memory is
allocated from the system, this pixmap cannot be involved in GPU accelerated option.
The number of pitch bytes used to access the pixmap memory may be different
depending on whether it was allocated from GPU accessible memory or from the system.
Once the memory for X pixmap has been allocated, no matter it is from GPU accessible
memory or from the system, the pixmap is locked and can never migrate to other type of
memory. Pixmap migration from GPU accessible memory to system memory is not
necessary since a system virtual address is always available for GPU accessible memory.
Pixmap migration from system memory to GPU accessible memory is not currently
implemented, but would only help in situations where there was insufficient GPU
accessible memory at initial allocation. More memory, however, becomes available
(through de-allocation) at a later time.
The GPU accessible memory pitch (horizontal) alignment for the GC320 is 8 pixels.
All of the memory allocated for
/dev/fb0
is made available to an internal linear offscreen
memory manager based on the one used in EXA. The portion of this memory beyond the
screen memory is available for allocation of X pixmap, where this memory area is GPU
accessible. The amount of memory allocated to
/dev/fb0
needs to be several MB more
than the amount needed for the screen. The actual amount needed depends on the number
of X-Windows and pixmaps used, the possible usage of X pixmaps as textures, and
whether X-Windows are using the XComposite extension.
Software Operation
i.MX 6SoloLite Linux Reference Manual, Rev. L3.0.35_4.1.0, 09/2013
88 Freescale Semiconductor, Inc.