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Date: Fri, 8 Mar 2024 16:37:15 -0400
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Vineet Gupta <vgupta@kernel.org>, Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Hanjun Guo <guohanjun@huawei.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
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	Lu Baolu <baolu.lu@linux.intel.com>,
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	Matthew Rosato <mjrosato@linux.ibm.com>,
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	Jean-Philippe Brucker <jean-philippe@linaro.org>,
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	Frank Rowand <frowand.list@gmail.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
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	linux-acpi@vger.kernel.org, iommu@lists.linux.dev,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v3 6/7] iommu/dma: Centralise iommu_setup_dma_ops()
Message-ID: <20240308203715.GA9225@ziepe.ca>
References: <cover.1707493264.git.robin.murphy@arm.com>
 <202fcca3269201bc9c4a8198253f195433d0c4ff.1707493264.git.robin.murphy@arm.com>
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In-Reply-To: <202fcca3269201bc9c4a8198253f195433d0c4ff.1707493264.git.robin.murphy@arm.com>

On Fri, Feb 09, 2024 at 04:50:03PM +0000, Robin Murphy wrote:
> It's somewhat hard to see, but arm64's arch_setup_dma_ops() should only
> ever call iommu_setup_dma_ops() after a successful iommu_probe_device(),
> which means there should be no harm in achieving the same order of
> operations by running it off the back of iommu_probe_device() itself.
> This then puts it in line with the x86 and s390 .probe_finalize bodges,
> letting us pull it all into the main flow properly. As a bonus this lets
> us fold in and de-scope the PCI workaround setup as well.
> 
> At this point we can also then pull the call up inside the group mutex,
> and avoid having to think about whether iommu_group_store_type() could
> theoretically race and free the domain if iommu_setup_dma_ops() ran just
> *before* iommu_device_use_default_domain() claims it... Furthermore we
> replace one .probe_finalize call completely, since the only remaining
> implementations are now one which only needs to run once for the initial
> boot-time probe, and two which themselves render that path unreachable.
> 
> This leaves us a big step closer to realistically being able to unpick
> the variety of different things that iommu_setup_dma_ops() has been
> muddling together, and further streamline iommu-dma into core API flows
> in future.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> v2: Shuffle around to make sure the iommu_group_do_probe_finalize() case
>     is covered as well, with bonus side-effects as above.
> v3: *Really* do that, remembering the other two probe_finalize sites too.
> ---
>  arch/arm64/mm/dma-mapping.c  |  2 --
>  drivers/iommu/amd/iommu.c    |  8 --------
>  drivers/iommu/dma-iommu.c    | 18 ++++++------------
>  drivers/iommu/dma-iommu.h    | 14 ++++++--------
>  drivers/iommu/intel/iommu.c  |  7 -------
>  drivers/iommu/iommu.c        | 20 +++++++-------------
>  drivers/iommu/s390-iommu.c   |  6 ------
>  drivers/iommu/virtio-iommu.c | 10 ----------
>  include/linux/iommu.h        |  7 -------
>  9 files changed, 19 insertions(+), 73 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason