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Date:   Mon, 16 Jan 2023 12:33:44 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Vasant Hegde <vasant.hegde@amd.com>,
        Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>,
        Rob Clark <robdclark@gmail.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Yong Wu <yong.wu@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Orson Zhai <orsonzhai@gmail.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@gmail.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        iommu@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/5] iommu: Retire detach_dev callback
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On Mon, Jan 16, 2023 at 05:24:56PM +0100, Marek Szyprowski wrote:

> > The iommu core calls the driver's detach_dev domain op callback only when
> > a device is finished assigning to user space and
> > iommu_group_release_dma_owner() is called to return the device to the
> > kernel, where iommu core wants to set the default domain to the device but
> > the driver didn't provide one. The code looks like:
> >
> >          /*
> >           * New drivers should support default domains and so the detach_dev() op
> >           * will never be called. Otherwise the NULL domain represents some
> >           * platform specific behavior.
> >           */
> >          if (!new_domain) {
> >                  if (WARN_ON(!group->domain->ops->detach_dev))
> >                          return -EINVAL;
> >                  __iommu_group_for_each_dev(group, group->domain,
> >                                             iommu_group_do_detach_device);
> >                  group->domain = NULL;
> >                  return 0;
> >          }
> >
> > In other words, if the iommu driver provides default domains, the
> > .detach_dev callback will never be called; Otherwise, the .detach_dev
> > callback is actually called to return control back to the platform DMA
> > ops, other than detaching the domain from device.
> >
> > This series cleanups this by:
> >
> > - If the IOMMU driver provides default domains, remove .detach_dev
> >    callback.
> > - Adds a new set_platform_dma iommu op. Any IOMMU driver that doesn't
> >    provide default domain should implement set_platform_dma callback
> >    instead.
> > - Retire .detach_dev callback.
> >
> > This series originates from various discussion in the community. Thanks
> > to Jason, Robin and all others for their ideas.
> 
> I wonder how to handle the ARM 32bit case, which doesn't use the default 
> domain solution. Today, once this patchset has been merged to 
> linux-next, I've noticed that it broke booting of ARM 32bit Exynos based 
> boards.

It is supposed to work, can you help debug what went wrong?

Jason