[PATCH v4 1/8] arm64: mm: change IOMMU notifier action to attach DMA ops

[will.deacon@arm.com (Will Deacon)]

Hi Catalin,

On Fri, Jul 01, 2016 at 05:50:10PM +0100, Robin Murphy wrote:
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> 
> Current bus notifier in ARM64 (__iommu_attach_notifier)
> attempts to attach dma_ops to a device on BUS_NOTIFY_ADD_DEVICE
> action notification.
> 
> This will cause issues on ACPI based systems, where PCI devices
> can be added before the IOMMUs the devices are attached to
> had a chance to be probed, causing failures on attempts to
> attach dma_ops in that the domain for the respective IOMMU
> may not be set-up yet by the time the bus notifier is run.
> 
> Devices dma_ops do not require to be set-up till the matching
> device drivers are probed. This means that instead of running
> the notifier attaching dma_ops to devices (__iommu_attach_notifier)
> on BUS_NOTIFY_ADD_DEVICE action, it can be run just before the
> device driver is bound to the device in question (on action
> BUS_NOTIFY_BIND_DRIVER) so that it is certain that its IOMMU
> group and domain are set-up accordingly at the time the
> notifier is triggered.
> 
> This patch changes the notifier action upon which dma_ops
> are attached to devices and defer it to driver binding time,
> so that IOMMU devices have a chance to be probed and to register
> their bus notifiers before the dma_ops attach sequence for a
> device is actually carried out.
> 
> As a result we also no longer need worry about racing with
> iommu_bus_notifier(), or about retrying the queue in case devices
> were added too early on DT-based systems, so clean up the notifier
> itself plus the additional workaround from 722ec35f7fae ("arm64:
> dma-mapping: fix handling of devices registered before arch_initcall")
> 
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> [rm: get rid of other now-redundant bits]
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> 
> v4: No change.
> 
>  arch/arm64/mm/dma-mapping.c | 22 +++++-----------------
>  1 file changed, 5 insertions(+), 17 deletions(-)

Whilst this series is unlikely to make it for 4.8, this patch is
independent and it would be good to see it queued in the arm64 tree for
4.8, if possible. It shouldn't change anything on its own, but it's a
prerequisite for this series and anything on the IORT side from Lorenzo,
so it makes sense to me to keep the delta down if we can.

Will