Hello,
On 2014-10-27 11:51, Will Deacon wrote:
On Tue, Oct 14, 2014 at 01:53:59PM +0100, Laurent Pinchart wrote:
On Monday 22 September 2014 18:50:27 Will Deacon wrote:
On Mon, Sep 22, 2014 at 10:29:10AM +0100, Thierry Reding wrote:
Agreed. I wonder how useful it is to know the set of IOMMU instances
that each device can master through. Wouldn't it be more useful to keep
a list of master interfaces for each device? The set of IOMMU instances
can trivially be derived from that.
I'm struggling to think how that would look. What do you mean by `master
interfaces' in terms of the code we have in Linux? At the end of the day,
the list of IOMMU instances (i.e. iommu_dma_mapping) exists because you
and Laurent have use-cases involving devices mastering through multiple
IOMMUs. If it doesn't work for you, it might be best for you to send me
the patch ;)
Just for the record, I've brought up the topic of masters being served by
multiple IOMMUs, but don't have a use case for it (yet at least). I do have
masters served through multiple streams with separate stream IDs, but all by
the same IOMMU.
Ok. I spoke to Arnd, David and Joerg at LPC and the consensus was that the
DMA-mapping API should *not* be exposed to the details of masters that
master through multiple IOMMUs. Instead, that should be abstracted by the
device API by exposing that device as a single struct device.
So, that's certainly an area that needs more work and I'll drop the limited
support I'd cooked up from this patch set in the next version.
Great! That's more or less something I've already implemented on top of your
previous patchset, as I didn't have any good idea how to manage multiple
masters
separately. I'm waiting for your next update and I will rebase my
patches soon.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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