Re: [PATCH v5 0/5] iommu: Retire detach_dev callback

[Jason Gunthorpe <jgg@nvidia.com>]

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