Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu explicitly

From: Robin Murphy
Date: Tue Sep 10 2019 - 12:52:07 EST

On 10/09/2019 16:34, Rob Clark wrote:
On Tue, Sep 10, 2019 at 1:14 AM Joerg Roedel <joro@xxxxxxxxxx> wrote:

On Fri, Sep 06, 2019 at 02:44:01PM -0700, Rob Clark wrote:
@@ -674,7 +674,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)

list_add_tail(&device->list, &group->devices);
- if (group->domain)
+ if (group->domain && !(dev->driver && dev->driver->driver_manages_iommu))

Hmm, this code usually runs at enumeration time when no driver is
attached to the device. Actually it would be pretty dangerous when this
code runs while a driver is attached to the device. How does that change
make things work for you?

I was seeing this get called via the path driver_probe_device() ->
platform_dma_configure() -> of_dma_configure() -> of_iommu_configure()
-> iommu_probe_device() -> ...

The only cases I was seeing where dev->driver is NULL where a few
places that drivers call of_dma_configure() on their own sub-devices.
But maybe there are some other paths that I did not notice?

For the of_iommu flow, it very much depends on your DT layout and driver probe order as to whether you catch the "proper" call from iommu_bus_notifier()/iommu_bus_init() or the late "replay" from of_iommu_configure(). I wouldn't make any assumptions of consistency.