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

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Message-ID: <20250917135819.GA1391379@nvidia.com>
Date: Wed, 17 Sep 2025 10:58:19 -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 04:41:28PM +0300, Leon Romanovsky wrote:
> On Wed, Sep 17, 2025 at 08:32:48AM -0300, Jason Gunthorpe wrote:
> > On Wed, Sep 17, 2025 at 01:36:44PM +0300, Leon Romanovsky wrote:
> > > On Tue, Sep 16, 2025 at 03:46:17PM -0300, Jason Gunthorpe wrote:
> > > > On Tue, Sep 16, 2025 at 10:32:06AM +0300, Leon Romanovsky wrote:
> > > > > +	if (!dev->dma_coherent &&
> > > > > +	    !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO)))
> > > > > +		__dma_page_cpu_to_dev(phys_to_page(phys), offset, size, dir);
> > > > 
> > > > I'd keep going and get rid of the page here too, maybe as a second
> > > > patch in this series:
> > > 
> > > Thanks, it is always unclear how far to go with cleanups.
> > 
> > IMHO to maximally support what Matthew is working on I'd remove all
> > the struct page things and prefer the pfn/phys variations from the MM
> > side.
> 
> ok, my patches can be found here:
> https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=dmabuf-vfio
> 
> I converted "struct page" path from all archs with .map_page.

Yeah, that's right, I would split this into a few series

This group is all fairly trivial stuff that didn't use the struct
page or virt address at all:

 MIPS/jazzdma
 x86
 vdpa
 xen: swiotlb:  (though make a phys_to_xen_pfn() macro)

I'd also drop the ATTR_MMIO checks from x86 and jazzdma
since the code is obviously fine with any phys.

vdpa can support ATTR_MMIO with the same iommu prot MMIO adjustment,
that would be a good additional patch.

Then there are more conversions that don't use struct page or va but
are not so trivial

alpha
parisc

Then the last ones sparc/power are quite complicated and do use
__va/etc.

Jason