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Subject: Re: [PATCH] vhost: introduce vDPA based backend
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Gunthorpe <jgg@mellanox.com>
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From:   Jason Wang <jasowang@redhat.com>
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Date:   Thu, 6 Feb 2020 11:11:52 +0800
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On 2020/2/5 =E4=B8=8B=E5=8D=889:14, Michael S. Tsirkin wrote:
> On Wed, Feb 05, 2020 at 08:56:48AM -0400, Jason Gunthorpe wrote:
>> On Wed, Feb 05, 2020 at 03:50:14PM +0800, Jason Wang wrote:
>>>> Would it be better for the map/umnap logic to happen inside each dev=
ice ?
>>>> Devices that needs the IOMMU will call iommu APIs from inside the dr=
iver callback.
>>> Technically, this can work. But if it can be done by vhost-vpda it wi=
ll make
>>> the vDPA driver more compact and easier to be implemented.
>> Generally speaking, in the kernel, it is normal to not hoist code of
>> out drivers into subsystems until 2-3 drivers are duplicating that
>> code. It helps ensure the right design is used
>>
>> Jason
> That's up to the sybsystem maintainer really, as there's also some
> intuition involved in guessing a specific API is widely useful.
> In-kernel APIs are flexible, if we find something isn't needed we just
> drop it.
>

If I understand correctly. At least Intel (Ling Shan) and Brodcom (Rob)=20
doesn't want to deal with DMA stuffs in their driver.

Anyway since the DMA bus operations is optional, driver may still choose=20
to do DMA by itself if they want even if it requires platform IOMMU to wo=
rk.

Thanks