Re: DMA-API attr - DMA_ATTR_NO_KERNEL_MAPPING

[Robin Murphy]

On 01/07/2019 18:47, Pankaj Suryawanshi wrote:
> > If you want a kernel mapping, *don't* explicitly request not to have a
> > kernel mapping in the first place. It's that simple.
>
> Do you mean do not use dma-api ? because if i used dma-api it will give you
> mapped virtual address.
> or i have to use directly cma_alloc() in my driver. // if i used this
> approach i need to reserved more vmalloc area.

No, I mean just call dma_alloc_attrs() normally *without* adding the 
DMA_ATTR_NO_KERNEL_MAPPING flag. That flag means "I never ever want to 
make CPU accesses to this buffer from the kernel" - that is clearly not 
the case for your code, so it is utterly nonsensical to still pass the 
flag but try to hack around it later.

Robin.