[Linaro-mm-sig] [PATCH 7/8] common: dma-mapping: change alloc/free_coherent method to more generic alloc/free_attrs

KyongHo Cho pullip.cho at samsung.com
Wed Jun 22 00:00:54 UTC 2011


2011/6/21 Marek Szyprowski <m.szyprowski at samsung.com>:
>
> You already got a reply that dropping dma_alloc_writecombine() is no
> go on ARM.
>
Yes.

> That's not a problem. Once we agree on dma_alloc_attrs(), the drivers
> can be changed to use DMA_ATTR_WRITE_COMBINE attribute. If the platform
> doesn't support the attribute, it is just ignored. That's the whole
> point of the attributes extension. Once a driver is converted to
> dma_alloc_attrs(), it can be used without any changes either on platforms
> that supports some specific attributes or the one that doesn't implement
> support for any of them.
>
I just worried that removing an existing construct is not a simple job.
You introduced 3 attributes: DMA_ATTR_WRITE_COMBINE, ***COHERENT and
***NO_KERNEL_VADDR

I replied earlier, I also indicated that write combining option for
dma_alloc_*() is required.
But it does not mean dma_map_ops must support that.
I think dma_alloc_writecombine() can be implemented regardless of dma_map_ops.

> Allocation is a separate operation from mapping to userspace. Mmap
> operation should just map the buffer (represented by a cookie of type
> dma_addr_t) to user address space.
>
> Note that some drivers (like framebuffer drivers for example) also
> needs to have both types of mapping - one for user space and one for
> kernel virtual space.

I meant that I think DMA_ATTR_NOKERNELVADDR is not required because
you also introduced mmap callback.



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