linux-kernel - Re: [PATCH v2 6/6] iommu: Delete iommu_dev_has

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Message-ID: <b31e8a41-3918-6b69-05af-45084e08bb7f@huawei.com>
Date:   Thu, 7 Jan 2021 09:13:50 +0000
From:   John Garry <john.garry@...wei.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>, <joro@...tes.org>,
        <will@...nel.org>
CC:     <iommu@...ts.linux-foundation.org>, <robin.murphy@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/6] iommu: Delete iommu_dev_has_feature()

On 07/01/2021 01:18, Lu Baolu wrote:
> On 1/6/21 9:35 PM, John Garry wrote:
>> Function iommu_dev_has_feature() has never been referenced in the tree,
>> and there does not appear to be anything coming soon to use it, so delete
>> it.
> 

Hi baolu,

> It will be used by the device driver which want to support the aux-
> domain capability, for example, below series is under discussion.
> 
> https://lore.kernel.org/linux-pci/160408357912.912050.17005584526266191420.stgit@djiang5-desk3.ch.intel.com/ 
> 

So I did check linux-iommu lore for recent references, above, but did 
not see this one - that really should have cc'ed linux-iommu list (which 
it didn't).

> 
> The typical use case is
> 
>          if (iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX)) {
>                  rc = iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_AUX);
>                  if (rc < 0) {
>                          dev_warn(dev, "Failed to enable aux-domain: 
> %d\n", rc);
>                          return rc;
>                  }
>          }
> 
> So please don't remove it.
> 

ok, fine. It also seems that this API has not had a user since it was 
introduced in v5.2.

Thanks,
John

Ps. I suppose a v3 series is not needed ATM - this patch can just be 
dropped.