On 2014-01-09 07:06, Hiremath, Vaibhav wrote: > I am seeing underflow issue on AM43x device if I use omapfb_vram argument. > Did you see this on OMAP? > > I am using "omapfb_vram=10M@0xA0000000", and I believe it is correct way of > usage.
Hmm ok... The AM4x seems to have issues anyway, as we're seeing underflows easily in other situations also. Well, there's a small difference in the allocation. The normal dma alloc uses dma_alloc_attrs() and passes DMA_ATTR_WRITE_COMBINE as a flag, whereas allocating from the absolute address just uses the piece of memory. I couldn't find how to set write-combine for the abs memory area. Then again, that's for CPU caching, so I don't see why it would affect DSS as such (but that's still something we should measure, cpu read/write perf for normal and abs allocation). The only thought I have is that somehow the reserved memory area is missing some configuration that is done for the rest of the memory. But that's purely a guess, this is totally out of my area of expertise... Vaibhav, just to be sure, can you run both with normal dma_alloc and with the reserve, and verify that the dispc register dumps are the same? I don't see how they could be different, but just to be sure. Tomi
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