[PATCHv2 2/4] mm: cma: Contiguous Memory Allocator added

[Marek Szyprowski]

Hello,

On Tuesday, July 27, 2010 2:59 PM Jonathan Corbet wrote:

> On Tue, 27 Jul 2010 14:45:58 +0200
> Marek Szyprowski <m.szyprowski at samsung.com> wrote:
> 
> > > How does one obtain the CPU address of this memory in order for the CPU
> > > to access it?
> >
> > Right, we did not cover such case. In CMA approach we tried to separate
> > memory allocation from the memory mapping into user/kernel space. Mapping
> > a buffer is much more complicated process that cannot be handled in a
> > generic way, so we decided to leave this for the device drivers. Usually
> > video processing devices also don't need in-kernel mapping for such
> > buffers at all.
> 
> Still...that *is* why I suggested an interface which would return both
> the DMA address and a kernel-space virtual address, just like the DMA
> API does...  Either that, or just return the void * kernel address and
> let drivers do the DMA mapping themselves.  Returning only the
> dma_addr_t address will make the interface difficult to use in many
> situations.

As I said, drivers usually don't need in-kernel mapping for video buffers.
Is there really a need for creating such mapping?

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center