Re: [PATCH v3 1/3] uio: introduce UIO_MEM_DMA_COHERENT type

[Chris Leech <cleech@redhat.com>]

Nilesh, 

On Tue, Jan 09, 2024 at 05:44:56PM +0530, Nilesh Javali wrote:
> +	ret = dma_mmap_coherent(&idev->dev,
> +				vma,
> +				addr,
> +				mem->dma_addr,
> +				vma->vm_end - vma->vm_start);

When I asked about the use of idev->dev here in the v2 posting, you
repled as follows.

> While the cnic loads, it registers the cnic_uio_dev->pdev->dev with
> uio and the uio attaches its device to cnic device as it's parent. So
> uio and cnic are attached to the same PCI device.

I still don't think the sysfs parent relationship is enough to get the
correct behavior out of the DMA APIs on all platforms, and
dma_mmap_coherent needs to be using the same device struct as
dma_alloc_coherent.

I had some testing done on an AMD system, where your v2 patch set was
failing with the iommu enabled, and my original changes were reported to
work.  And I believe these v3 patches are functionally the same.

- Chris