Re: IOVA allocation dependency between firmware buffer and remaining buffers

[Ajay kumar <ajaynumb@gmail.com>]

Can someone check this?

On Mon, Apr 20, 2020 at 9:24 PM Ajay kumar <ajaynumb@gmail.com> wrote:
>
> Hi All,
>
> I have an IOMMU master which has limitations as mentioned below:
> 1) The IOMMU master internally executes a firmware, and the firmware memory
> is allocated by the same master driver.
> The firmware buffer address should be of the lowest range than other address
> allocated by the device, or in other words, all the remaining buffer addresses
> should always be in a higher range than the firmware address.
> 2) None of the buffer addresses should go beyond 0xC000_0000
>
> example:
> If firmware buffer address is buf_fw = 0x8000_5000;
> All other addresses given to the device should be greater than
> (0x8000_5000 + firmware size) and less than 0xC000_0000
>
> Currently, this is being handled with one of the below hacks:
> 1) By keeping dma_mask in lower range while allocating firmware buffer,
> and then increasing the dma_mask to higher range for other buffers.
> 2) By reserving IOVA for firmware at the lowest range and creating direct mappings for the same.
>
> I want to know if there is a better way this can be handled with current framework,
> or if anybody is facing similar problems with their devices,
> please share how it is taken care.
>
> I also think there should be some way the masters can specify the IOVA
> range they want to limit to for current allocation.
> Something like a new iommu_ops callback like below:
> limit_iova_alloc_range(dev, iova_start, iova_end)
>
> And, in my driver, the sequence will be:
> limit_iova_alloc_range(dev, 0x0000_0000, 0x1000_0000); /* via helpers */
> alloc( ) firmware buffer using DMA API
> limit_iova_alloc_range(dev, 0x1000_0000, 0xC000_0000); /* via helpers */
> alloc( ) other buffers using DMA API
>
> Thanks,
> Ajay Kumar