[dpdk-dev] [PATCH v10 3/9] linuxapp/eal_pci: get iommu class

[santosh]

On Wednesday 11 October 2017 12:34 PM, Tan, Jianfeng wrote:
>
>> -----Original Message-----
>> From: santosh [mailto:santosh.shukla at caviumnetworks.com]
>> Sent: Wednesday, October 11, 2017 1:38 PM
>> To: Tan, Jianfeng; olivier.matz at 6wind.com; dev at dpdk.org
>> Cc: thomas at monjalon.net; jerin.jacob at caviumnetworks.com;
>> hemant.agrawal at nxp.com; aconole at redhat.com;
>> stephen at networkplumber.org; Burakov, Anatoly; gaetan.rivet at 6wind.com;
>> shreyansh.jain at nxp.com; Richardson, Bruce; Gonzalez Monroy, Sergio;
>> maxime.coquelin at redhat.com
>> Subject: Re: [dpdk-dev] [PATCH v10 3/9] linuxapp/eal_pci: get iommu class
>>
>>
>> On Wednesday 11 October 2017 11:01 AM, Tan, Jianfeng wrote:
>>>
>>> On 10/11/2017 12:43 PM, santosh wrote:
>>>> On Wednesday 11 October 2017 07:17 AM, Tan, Jianfeng wrote:
>>>>> Hi,
>>>>>
>>>>> Nice patch series. But I still have a small question about below flag.
>>>>>
>>>>>
>>>>> On 10/6/2017 7:03 PM, Santosh Shukla wrote:
>>>>>> Get iommu class of PCI device on the bus and returns preferred iova
>>>>>> mapping mode for that bus.
>>>>>>
>>>>>> Patch also introduces RTE_PCI_DRV_IOVA_AS_VA drv flag.
>>>>>> Flag used when driver needs to operate in iova=va mode.
>>>>>>
>>>>> Does this flag indicate a must to use VA as IOVA, or a nice-to-have one?
>> In detail, above commit log says, "needs to operate in iova=va mode", but
>> the comment in the patch indicates this flag means "driver supports IOVA as
>> VA".
>>>>> If it's the latter case, I would suppose all drivers support to use VA as
>> IOVA, if the NICs are binded to vfio-pci (iommu mode). Please correct me if
>> I'm wrong.
>>>> - Any iommu backed pmd could choose to use this flag.
>>> But if this is characterized by assumption for all PMDs, why do we trouble
>> to introduce this flag.
>> to hint bus layer about iova=va mapping choice for _this_ driver and default
>> is iova=pa.
>>
> So that sounds if this flag is set by some PMD, we must use iova=va.
>
> Then how about we enable this, iova=va, if only all PCI devices are binded to vfio-pci (iommu mode)?

Right, same I proposed (I guess) in v2 such that iova bus autodetecting in case see all device bound
to vfio-pci then autoselect iova=va, in v3 series (I guess) discussion: it was concluded that
better to send hint from driver. Refer work history, though iova bus still does said
auto-detection.

Thanks.