Re: [PATCH v3 08/13] iommu/arm-smmu-v3: Propate ssid_bits

On Tue, Dec 17, 2019 at 06:07:26PM +0100, Auger Eric wrote:

Hi Jean,

On 12/9/19 7:05 PM, Jean-Philippe Brucker wrote:

s/Propate/Propagate in the commit title.

quoted

Now that we support substream IDs, initialize s1cdmax with the number of
SSID bits supported by a master and the SMMU.

Context descriptor tables are allocated once for the first master
attached to a domain. Therefore attaching multiple devices with
different SSID sizes is tricky, and we currently don't support it.

As a future improvement it would be nice to at least support attaching a
SSID-capable device to a domain that isn't using SSID, by reallocating
the SSID table.

Isn't that use case relevant (I mean using both devices in a non SSID
use case). For platform devices you can work this around with FW but for
PCI devices?

Normally each device gets its own domain. Especially since PASID is a PCI
Express capability, I expect them to be properly isolated with ACS, each
with its own IOMMU group. So I don't think this is too relevant for the
moment, it would be a quirk for a broken system.

Thanks,
Jean

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