OMAP Framebuffer memory allocation and mapping

[Tomi Valkeinen <tomi.valkeinen@nokia.com>]

Hi,

I have a couple of questions regarding the memory management for the new
display subsystem.

The new DSS allocates memory with dma_alloc_writecombine() and mmaps it
to user space with dma_mmap_writecombine(). Allocation is done when
omapfb starts up. Normally memory gets very quickly too fragmented for
dma_alloc_writecombine() to work, but setting
CONFIG_FB_OMAP_CONSISTENT_DMA_SIZE helps this.

However, even when CONFIG_FB_OMAP_CONSISTENT_DMA_SIZE is set to 14, I
am, for some reason, not able to allocate 1280x1024x4 (~5.2M)
framebuffer. Could the consistent DMA area be already too fragmented, or
is there some size limit there?

There's also support to allocate fb memory in very early phase with
reserve_bootmem(), which needs a predefined physical address and size
that can come from the bootloader. I've been looking at the old DSS to
see how this memory should be mapped, but I haven't been able to get it
to work. It looks like the DSS DMA and the user space have a bit
different view of the memory, so my assumption is that there's some
caching or similar being done.

So how to setup the memory gotten from reserve_bootmem() (or
alloc_bootmem()) so that it would work the same way as
dma_alloc_writecombine()'s memory?

And generally: any other ideas how to improve the memory management of
the DSS?

 Tomi