Re: [PATCH v3 01/18] iommu: Add device dma ownership set/release interfaces

From: Christoph Hellwig <hch@infradead.org>
To: Joerg Roedel <joro@8bytes.org>
Cc: Lu Baolu <baolu.lu@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Christoph Hellwig <hch@infradead.org>,
	Kevin Tian <kevin.tian@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Dan Williams <dan.j.williams@intel.com>,
	rafael@kernel.org, Diana Craciun <diana.craciun@oss.nxp.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Eric Auger <eric.auger@redhat.com>, Liu Yi L <yi.l.liu@intel.com>,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Stuart Yoder <stuyoder@gmail.com>,
	Laurentiu Tudor <laurentiu.tudor@nxp.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Li Yang <leoyang.li@nxp.com>, Dmitry Osipenko <digetx@gmail.com>,
	iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 01/18] iommu: Add device dma ownership set/release interfaces
Date: Mon, 6 Dec 2021 06:29:49 -0800	[thread overview]
Message-ID: <Ya4eXZtdMGhEP7GO@infradead.org> (raw)
In-Reply-To: <Ya4Ru/GtILJYzI6j@8bytes.org>

On Mon, Dec 06, 2021 at 02:35:55PM +0100, Joerg Roedel wrote:
> >                 enum iommu_dma_owner type, void *owner_cookie);
> >         void iommu_device_release_dma_owner(struct device *dev,
> >                 enum iommu_dma_owner type);
> 
> It the owner is a group-wide setting, it should be called with the group
> instead of the device. I have seen the group-specific funcitons are
> added later, but that leaves the question why the device-specific ones
> are needed at all.

They aren't really.  A lot of bus drivers need helpers to set/release
the dma API domain if there is an iommu group, but tegra which actually
sets a non-default value would be much better off with just open coding
them.

> > @@ -621,6 +624,7 @@ struct iommu_group *iommu_group_alloc(void)
> >  	INIT_LIST_HEAD(&group->devices);
> >  	INIT_LIST_HEAD(&group->entry);
> >  	BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
> > +	group->dma_owner = DMA_OWNER_NONE;
> 
> 
> DMA_OWNER_NONE is also questionable. All devices are always in one
> domain, and the default domain is always the one used for DMA-API, so
> why isn't the initial value DMA_OWNER_DMA_API?

The interesting part is the suppress_auto_claim_dma_owner flag, but it
might make more sense to release the dma API ownership for that rather
than requesting it if it is not set.