linux-kernel - Re: [PATCH v3 3/4] ARM: dma-mapping: Switch to physical address mapping callbacks

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Message-ID: <20250917190846.GE1391379@nvidia.com>
Date: Wed, 17 Sep 2025 16:08:46 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v3 3/4] ARM: dma-mapping: Switch to physical address
 mapping callbacks

On Wed, Sep 17, 2025 at 09:46:25PM +0300, Leon Romanovsky wrote:
> Let's take as an example MIPS/jazzdma, should we call to vdma_alloc()
> in DMA_ATTR_MMIO case?

Yes, that is right, this is an iommu, so it has to be programmed.

> or directly return "phys" as it is done in other
> architectures?

Which?

> > vdpa can support ATTR_MMIO with the same iommu prot MMIO adjustment,
> > that would be a good additional patch.
> 
> There is "bounce page" in VDPA, it sounds like swiotlb to me, which
> doesn't work with MMIO.

Oh OK, it eventually does call pfn_to_page().. This isn't the case I
thought it was, there is another one that just routes to iommu_map

Jason