From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>, David Airlie <airlied@linux.ie>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Jacob jun Pan <jacob.jun.pan@intel.com>,
Christoph Hellwig <hch@infradead.org>,
Alex Williamson <alex.williamson@redhat.com>,
Thierry Reding <thierry.reding@gmail.com>,
Ben Skeggs <bskeggs@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
Jonathan Hunter <jonathanh@nvidia.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops
Date: Tue, 25 Jan 2022 11:00:46 -0400 [thread overview]
Message-ID: <20220125150046.GK84788@nvidia.com> (raw)
In-Reply-To: <ab09f75c-08cc-1845-9aa7-81fed779d636@arm.com>
On Tue, Jan 25, 2022 at 02:23:52PM +0000, Robin Murphy wrote:
> On 2022-01-25 06:27, Lu Baolu wrote:
> Where it's just about which operations are valid for which domains, it's
> even simpler for the core interface wrappers to validate the domain type,
> rather than forcing drivers to implement multiple ops structures purely for
> the sake of having different callbacks populated. We already have this in
> places, e.g. where iommu_map() checks for __IOMMU_DOMAIN_PAGING.
In my experience it is usually much clearer to directly test the op
for NULL to know if a feature is supported than to invent flags to do
the same test. eg ops->map/etc == NULL means no paging.
I think we should not be afraid to have multiple ops in drivers for
things that are actually different in the driver. This is usually a
net win vs tying to handle all the cases with different 'if' flows.
eg identity domains and others really would ideally eventually have a
NULL ops for map/unmap too.
The 'type' should conceptually be part of the ops, not the mutable
struct - but we don't have to get there all at once.
> Paging domains are also effectively the baseline level of IOMMU API
> functionality. All drivers support them, and for the majority of drivers
> it's all they will ever support. Those drivers really don't benefit from any
> of the churn and boilerplate in this patch as-is, and it's so easy to
> compromise with a couple of lines of core code to handle the common case by
> default when the driver *isn't* one of the handful which ever actually cares
> to install their own per-domain ops. Consider how much cleaner this patch
> would look if the typical driver diff could be something completely minimal
> like this:
It is clever, but I'm not sure if hoisting a single assignment out of
the driver is worth the small long term complexity of having different
driver flows?
Jason
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next prev parent reply other threads:[~2022-01-25 15:00 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-24 7:10 [PATCH 0/7] iommu cleanup and refactoring Lu Baolu
2022-01-24 7:10 ` [PATCH 1/7] iommu/vt-d: Remove guest pasid related callbacks Lu Baolu
2022-01-24 9:25 ` Christoph Hellwig
2022-01-24 7:10 ` [PATCH 2/7] iommu: Remove guest pasid related interfaces and definitions Lu Baolu
2022-01-24 9:26 ` Christoph Hellwig
2022-01-24 7:10 ` [PATCH 3/7] iommu/vt-d: Remove aux-domain related callbacks Lu Baolu
2022-01-24 9:26 ` Christoph Hellwig
2022-01-24 7:10 ` [PATCH 4/7] iommu: Remove aux-domain related interfaces and iommu_ops Lu Baolu
2022-01-24 9:27 ` Christoph Hellwig
2022-01-24 7:11 ` [PATCH 5/7] drm/nouveau/device: Get right pgsize_bitmap of iommu_domain Lu Baolu
2022-01-24 9:29 ` Christoph Hellwig
2022-01-25 2:59 ` Lu Baolu
2022-01-24 7:11 ` [PATCH 6/7] iommu: Use right way to retrieve iommu_ops Lu Baolu
2022-01-24 9:32 ` Christoph Hellwig
2022-01-25 3:01 ` Lu Baolu
2022-01-24 9:48 ` Tian, Kevin
2022-01-25 3:04 ` Lu Baolu
2022-01-24 17:36 ` Jason Gunthorpe via iommu
2022-01-25 3:18 ` Lu Baolu
2022-01-25 0:20 ` Robin Murphy
2022-01-25 3:54 ` Lu Baolu
2022-01-24 7:11 ` [PATCH 7/7] iommu: Add iommu_domain::domain_ops Lu Baolu
2022-01-24 9:37 ` Christoph Hellwig
2022-01-24 17:24 ` Jason Gunthorpe via iommu
2022-01-25 4:43 ` Lu Baolu
2022-01-25 4:42 ` Lu Baolu
2022-01-24 9:58 ` Tian, Kevin
2022-01-24 10:16 ` Jean-Philippe Brucker
2022-01-24 16:33 ` Jason Gunthorpe via iommu
2022-01-26 9:41 ` Jean-Philippe Brucker
2022-01-24 17:17 ` Jason Gunthorpe via iommu
2022-01-25 4:59 ` Lu Baolu
2022-01-25 12:37 ` Jason Gunthorpe via iommu
2022-01-24 17:55 ` Jason Gunthorpe via iommu
2022-01-25 5:04 ` Lu Baolu
2022-01-25 0:57 ` Robin Murphy
2022-01-25 6:27 ` Lu Baolu
2022-01-25 14:23 ` Robin Murphy
2022-01-25 15:00 ` Jason Gunthorpe via iommu [this message]
2022-01-24 9:46 ` [PATCH 0/7] iommu cleanup and refactoring Tian, Kevin
2022-01-24 17:44 ` Jason Gunthorpe via iommu
2022-01-25 1:11 ` Tian, Kevin
2022-01-25 14:48 ` Robin Murphy
2022-01-25 15:16 ` Jason Gunthorpe via iommu
2022-01-26 1:51 ` Lu Baolu
2022-01-26 13:27 ` Jason Gunthorpe via iommu
2022-01-26 14:00 ` Robin Murphy
2022-02-08 1:32 ` Lu Baolu
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