Re: Tegra DRM device tree bindings

Hi Lucas,

On Wed, 27 Jun 2012 17:59:55 +0200
Lucas Stach [off-list ref] wrote:

quoted

quoted

quoted

quoted

Rather than introducing a new property, how about using
"coherent_pool=??M" in the kernel command line if necessary? I think
that this carveout size depends on the system usage/load.

I was hoping that we could get away with using the CMA and perhaps
initialize it based on device tree content. I agree that the carveout
size depends on the use-case, but I still think it makes sense to
specify it on a per-board basis.

DRM driver doesn't know if it uses CMA or not, because DRM only uses
DMA API.

So how is the DRM supposed to allocate buffers? Does it call the
dma_alloc_from_contiguous() function to do that? I can see how it is
used by arm_dma_ops but how does it end up in the driver?

As I said before the DMA API is not a good fit for graphics drivers.
Most of the DMA buffers used by graphics cores are long lived and big,
so we need a special pool to alloc from to avoid eating all contiguous
address space, as DMA API does not provide shrinker callbacks for
clients using large amount of memory.

For contiguious address space shortage issue in DMA API, I think that
DMABUF framework can handle?

If so, is there any good example for DMABUF used in DRM?