[dpdk-dev] [PATCH 00/10] Infrastructure to detect iova mapping on the bus

[Thomas Monjalon]

Hi Santosh,
Let's try to make this proposal clearer in order to have some reviews.

08/06/2017 13:05, Santosh Shukla:
> 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,

Some readers may not know IOVA: IO Virtual address.
Some explanations:
	https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt
	http://vfio.blogspot.fr/2014/08/iommu-groups-inside-and-out.html

It must be said that SMMU is equivalent to IOMMU for ARM:
	https://developer.arm.com/products/system-ip/system-controllers/system-memory-management-unit

> when packet receives from the Ethernet device, it is the IOVA address
> (which is PA in existing scheme).

You mean that we are currently using only Physical Address (PA)?

> Mapping IOVA as PA is expensive on those HW, where every packet
> needs to be converted to VA from PA/IOVA.

Please, could you explain how and where addresses are converted currently?

> 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).

I think you should better describe these modes and how they behave.

> To achieve that, two global APIs introduced:
> - rte_bus_get_iommu_class
> - rte_pci_get_iommu_class
> 
> Return values for those APIs are:
> enum rte_iova_mod {
>         RTE_IOVA_DC, /* Don't care */
>         RTE_IOVA_PA,
>         RTE_IOVA_VA
> }
> 
> Those are the bus policy for selecting IOVA mode. In case user
> want to override bus IOVA mapping then added an EAL option
> "--iova-mode=<string>". User to pass string format 'pa' --> IOVA_PA,
> 'va' --> IOVA_VA.
> 
> To support new eal option, adding global API:
> - rte_eal_iova_mode
> 
> Patch Summary:
> 2) 1st - 2th patch: Adds infrastructure in linuxapp and bsdapp
> layer.
> 1) 3rd patch: Introduces global bus api named rte_bus_get_iommu_class.
> 3) 4th patch: Add new eal option called --iova-mode=<mode-string>.
> 4) 5th - 6th patch: Logic to detect iova scheme.
> 5) 9th patch: Check IOVA mode before programing vfio dma_map.iova.
> Default scheme is IOVA_PA.
> 6) 10th-12th patch: Check for IOVA_VA mode in below APIs
>         - rte_mem_virt2phy
>         - rte_mempool_virt2phy
>         - rte_malloc_virt2phy
> If set then return paddr=vaddr, else return value from default
> implementation.