bcm2708_fb: DMA acceleration for fb_copyarea
Based on http://www.raspberrypi.org/phpBB3/viewtopic.php?p=62425#p62425 Also used Simon's dmaer_master module as a reference for tweaking DMA settings for better performance. For now busylooping only. IRQ support might be added later. With non-overclocked Raspberry Pi, the performance is ~360 MB/s for simple copy or ~260 MB/s for two-pass copy (used when dragging windows to the right). In the case of using DMA channel 0, the performance improves to ~440 MB/s. For comparison, VFP optimized CPU copy can only do ~114 MB/s in the same conditions (hindered by reading uncached source buffer). Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
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