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From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: andmike@us.ibm.com, sukadev@linux.vnet.ibm.com,
	mdroth@linux.vnet.ibm.com, b.zolnierkie@samsung.com,
	benh@kernel.crashing.org, jasowang@redhat.com, aik@linux.ibm.com,
	Ram Pai <linuxram@us.ibm.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org, paulus@ozlabs.org,
	iommu@lists.linux-foundation.org, paul.burton@mips.com,
	mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, hch@lst.de,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr()
Date: Tue, 15 Oct 2019 09:31:04 +0200
Message-ID: <20191015073104.GA32252@lst.de> (raw)
In-Reply-To: <37609731-5539-b906-aa94-2ef0242795ac@arm.com>

On Mon, Oct 14, 2019 at 11:29:24AM +0100, Robin Murphy wrote:
>> However, I would like to see the commit message (and maybe the inline
>> comments) expanded a bit on what the distinction here is about.  Some
>> of the text from the next patch would be suitable, about DMA addresses
>> usually being in a different address space but not in the case of
>> bounce buffering.
>
> Right, this needs a much tighter definition. "DMA address happens to be a 
> valid physical address" is true of various IOMMU setups too, but I can't 
> believe it's meaningful in such cases.
>
> If what you actually want is "DMA is direct or SWIOTLB" - i.e. "DMA address 
> is physical address of DMA data (not necessarily the original buffer)" - 
> wouldn't dma_is_direct() suffice?

It would.  But drivers have absolutely no business knowing any of this.
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  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-12  1:25 [PATCH 0/2] virtio: Support encrypted memory on powerpc secure guests Ram Pai
2019-10-12  1:25 ` [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr() Ram Pai
2019-10-12  1:25   ` [PATCH 2/2] virtio_ring: Use DMA API if memory is encrypted Ram Pai
2019-10-14  4:52     ` David Gibson
2019-10-15  7:35     ` Christoph Hellwig
2019-10-16  7:55       ` Ram Pai
2019-10-17  2:33       ` Jason Wang
2019-10-21  8:36       ` David Gibson
2019-10-14  4:51   ` [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr() David Gibson
2019-10-14 10:29     ` Robin Murphy
2019-10-15  7:30       ` Ram Pai
2019-10-15  7:31       ` Christoph Hellwig [this message]
2019-10-12  1:36 ` [PATCH 0/2] virtio: Support encrypted memory on powerpc secure guests Ram Pai

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