Re: DMA-API attr - DMA_ATTR_NO_KERNEL_MAPPING

[Pankaj Suryawanshi <pankajssuryawanshi@gmail.com>]

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[CC: linux kernel and Vlastimil Babka]

On Wed, Jun 26, 2019 at 10:11 PM Pankaj Suryawanshi <
pankajssuryawanshi@gmail.com> wrote:

> Hello,
>
> I am writing driver in which I used DMA_ATTR_NO_KERNEL_MAPPING attribute
> for cma allocation using dma_alloc_attr(), as per kernel docs
> https://www.kernel.org/doc/Documentation/DMA-attributes.txt  buffers
> allocated with this attribute can be only passed to user space by calling
> dma_mmap_attrs().
>
> how can I mapped in kernel space (after dma_alloc_attr with
> DMA_ATTR_NO_KERNEL_MAPPING ) ?
>
> For example.
>
> 1. virtual_addr = dma_alloc_attr(device, size,, phys, GFP_KERNEL,
> DMA_ATTR_NO_KERNEL_MAPPING );
> 2. Now i can use phys for driver as physical address and i am using in
> drivers, working fine.
> 3. Now i want to use virtual address in kernel space(in some cases virtual
> address required in my driver), not allow to use virtual_addr in kernel
> space because DMA_ATTR_NO_KERNEL_MAPPING, How can i mapped again to
> kernel space ?
>
> How can i used DMA_ATTR_NO_KERNEL_MAPPING  and mapped some area for
> kernel space when needed ?
>
> Is there any apis available ? or improvement is required in linux kernel
> dma-apis ?
>
> Regards,
> Pankaj
>

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