Re: [PATCH 02/11] driver core: Set DMA ownership during driver bind/unbind

From: Christoph Hellwig <hch@infradead.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Ashok Raj <ashok.raj@intel.com>,
	kvm@vger.kernel.org, rafael@kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Cornelia Huck <cohuck@redhat.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Christoph Hellwig <hch@infradead.org>,
	Will Deacon <will@kernel.org>,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Diana Craciun <diana.craciun@oss.nxp.com>
Subject: Re: [PATCH 02/11] driver core: Set DMA ownership during driver bind/unbind
Date: Mon, 15 Nov 2021 10:15:07 -0800	[thread overview]
Message-ID: <YZKjq3sXb9+UTDSz@infradead.org> (raw)
In-Reply-To: <20211115155613.GA2388278@nvidia.com>

On Mon, Nov 15, 2021 at 11:56:13AM -0400, Jason Gunthorpe wrote:
> drivers/base/platform.c:        .dma_configure  = platform_dma_configure,
> drivers/bus/fsl-mc/fsl-mc-bus.c:        .dma_configure  = fsl_mc_dma_configure,
> drivers/pci/pci-driver.c:       .dma_configure  = pci_dma_configure,
> drivers/gpu/host1x/bus.c:       .dma_configure = host1x_dma_configure,
> 
> Other than host1x they all work with VFIO.
> 
> Also, there is no bus->dma_unconfigure() which would be needed to
> restore the device as well.
> 
> So, would you rather see duplicated code into the 4 drivers, and a new
> bus op to 'unconfigure dma'

The tend to mostly call into common helpers eventually.

> 
> Or, a 'dev_configure_dma()' function that is roughly:
> 
>         if (dev->bus->dma_configure) {
>                 ret = dev->bus->dma_configure(dev);
>                 if (ret)
>                         return ret;
>                 if (!drv->suppress_auto_claim_dma_owner) {
>                        ret = iommu_device_set_dma_owner(dev, DMA_OWNER_KERNEL,
>                                                         NULL);
>                        if (ret)
>                                ret;
>                 }
>          }
> 
> And a pair'd undo.

But that seems like an even better idea to me.  Even better with an
early return and avoiding the pointless indentation.
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