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Date:   Thu, 24 Feb 2022 08:58:36 +0000
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Subject: Re: [PATCH v6 01/11] iommu: Add dma ownership management interfaces
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To:     Lu Baolu <baolu.lu@linux.intel.com>,
        Jason Gunthorpe <jgg@nvidia.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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From:   Robin Murphy <robin.murphy@arm.com>
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On 2022-02-24 05:29, Lu Baolu wrote:
> On 2/24/22 1:16 PM, Lu Baolu wrote:
>> Hi Robin and Jason,
>>
>> On 2/24/22 2:02 AM, Jason Gunthorpe wrote:
>>> On Wed, Feb 23, 2022 at 06:00:06PM +0000, Robin Murphy wrote:
>>>
>>>> ...and equivalently just set owner_cnt directly to 0 here. I don't 
>>>> see a
>>>> realistic use-case for any driver to claim the same group more than 
>>>> once,
>>>> and allowing it in the API just feels like opening up various potential
>>>> corners for things to get out of sync.
>>> I am Ok if we toss it out to get this merged, as there is no in-kernel
>>> user right now.
>>
>> So we don't need the owner pointer in the API anymore, right?
> 
> Oh, NO.
> 
> The owner token represents that the group has been claimed for user
> space access. And the default domain auto-attach policy will be changed
> accordingly.
> 
> So we still need this. Sorry for the noise.

Exactly. In fact we could almost go the other way, and rename owner_cnt 
to dma_api_users and make it mutually exclusive with owner being set, 
but that's really just cosmetic. It's understandable enough as-is that 
owner_cnt > 0 with owner == NULL represents implicit DMA API ownership.

Cheers,
Robin.