From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: Re: [PATCH 00/10] Infrastructure to detect iova mapping
 on the bus
Date: Wed, 5 Jul 2017 11:30:37 +0200
Message-ID: <59355fcd-0da3-9625-8a0c-dc8c4d44c127@redhat.com>
References: <20170608110513.22548-1-santosh.shukla@caviumnetworks.com>
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Cc: jerin.jacob@caviumnetworks.com, hemant.agrawal@nxp.com,
 shreyansh.jain@nxp.com, gaetan.rivet@6wind.com
To: Santosh Shukla <santosh.shukla@caviumnetworks.com>, thomas@monjalon.net,
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On 06/08/2017 01:05 PM, Santosh Shukla wrote:
> Q) Why do we need such infrastructure?
> 
> A) Some NPU hardware like OCTEONTX follows push model to get the packet
> from the pktio device. Where packet allocation and freeing done
> by the HW. Since HW can operate only on IOVA with help of SMMU/IOMMU,
> when packet receives from the Ethernet device, it is the IOVA address
> (which is PA in existing scheme).
> 
> Mapping IOVA as PA is expensive on those HW, where every packet
> needs to be converted to VA from PA/IOVA.
> 
> This patchset proposes the method to autodetect the preferred
> IOVA mode for a device. Summary of IOVA scheme:
> - If all the devices are iommu capable and support IOMMU
>    capable driver then selects IOVA_VA.
> - If any of the devices are non-iommu then use default IOVA
>    scheme ie. IOVA_PA.
> - If no device found then IOVA scheme would be
>    IOVA_DC (Don't care).

Isn't it possible to have a per-device granularity?
For example, with virt case, having a physical NIC using VFIO with
iommu, and virtio devices with noiommu.

If the physical NIC prefers working with VAs, why forcing it to use
PAs? Maybe I missed a limitation though.

Cheers,
Maxime