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Message-ID: <20250831131250.GC10073@unreal>
Date: Sun, 31 Aug 2025 16:12:50 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
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Subject: Re: [PATCH v4 09/16] dma-mapping: handle MMIO flow in
dma_map|unmap_page
On Thu, Aug 28, 2025 at 12:17:30PM -0300, Jason Gunthorpe wrote:
> On Tue, Aug 19, 2025 at 08:36:53PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> >
> > Extend base DMA page API to handle MMIO flow and follow
> > existing dma_map_resource() implementation to rely on dma_map_direct()
> > only to take DMA direct path.
>
> I would reword this a little bit too
>
> dma-mapping: implement DMA_ATTR_MMIO for dma_(un)map_page_attrs()
>
> Make dma_map_page_attrs() and dma_map_page_attrs() respect
> DMA_ATTR_MMIO.
>
> DMA_ATR_MMIO makes the functions behave the same as dma_(un)map_resource():
> - No swiotlb is possible
> - Legacy dma_ops arches use ops->map_resource()
> - No kmsan
> - No arch_dma_map_phys_direct()
>
> The prior patches have made the internl funtions called here support
> DMA_ATTR_MMIO.
>
> This is also preparation for turning dma_map_resource() into an inline
> calling dma_map_phys(DMA_ATTR_MMIO) to consolidate the flows.
>
> > @@ -166,14 +167,25 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
> > return DMA_MAPPING_ERROR;
> >
> > if (dma_map_direct(dev, ops) ||
> > - arch_dma_map_phys_direct(dev, phys + size))
> > + (!is_mmio && arch_dma_map_phys_direct(dev, phys + size)))
> > addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
>
> PPC is the only user of arch_dma_map_phys_direct() and it looks like
> it should be called on MMIO memory. Seems like another inconsistency
> with map_resource. I'd leave it like the above though for this series.
>
> > else if (use_dma_iommu(dev))
> > addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
> > - else
> > + else if (is_mmio) {
> > + if (!ops->map_resource)
> > + return DMA_MAPPING_ERROR;
>
> Probably written like:
>
> if (ops->map_resource)
> addr = ops->map_resource(dev, phys, size, dir, attrs);
> else
> addr = DMA_MAPPING_ERROR;
I'm big fan of "if (!ops->map_resource)" coding style and prefer to keep it.
>
> As I think some of the design here is to run the trace even on the
> failure path?
Yes, this is how it worked before.
>
> Otherwise looks OK
>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
>
> Jason
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