Messages in this thread | | | Date | Mon, 24 Jun 2019 10:55:50 -0300 | From | Jason Gunthorpe <> | Subject | Re: [RFC PATCH 00/28] Removing struct page from P2PDMA |
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On Mon, Jun 24, 2019 at 03:50:24PM +0200, Christoph Hellwig wrote: > On Mon, Jun 24, 2019 at 10:46:41AM -0300, Jason Gunthorpe wrote: > > BTW, it is not just offset right? It is possible that the IOMMU can > > generate unique dma_addr_t values for each device?? Simple offset is > > just something we saw in certain embedded cases, IIRC. > > Yes, it could. If we are trying to do P2P between two devices on > different root ports and with the IOMMU enabled we'll generate > a new bus address for the BAR on the other side dynamically everytime > we map.
Even with the same root port if ACS is turned on could behave like this.
It is only a very narrow case where you can take shortcuts with dma_addr_t, and I don't think shortcuts like are are appropriate for the mainline kernel..
Jason
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