On Monday 01 September 2014 09:52:19 Thierry Reding wrote: > On Fri, Aug 29, 2014 at 04:54:24PM +0100, Will Deacon wrote: > > IOMMU drivers must be initialised before any of their upstream devices, > > otherwise the relevant iommu_ops won't be configured for the bus in > > question. To solve this, a number of IOMMU drivers use initcalls to > > initialise the driver before anything has a chance to be probed. > > > > Whilst this solves the immediate problem, it leaves the job of probing > > the IOMMU completely separate from the iommu_ops to configure the IOMMU, > > which are called on a per-bus basis and require the driver to figure out > > exactly which instance of the IOMMU is being requested. In particular, > > the add_device callback simply passes a struct device to the driver, > > which then has to parse firmware tables or probe buses to identify the > > relevant IOMMU instance. > > > > This patch takes the first step in addressing this problem by adding an > > early initialisation pass for IOMMU drivers, giving them the ability to > > set some per-instance data on their of_node. This data can then be > > passed back to a new add_device function (added in a later patch) to > > identify the IOMMU instance in question. > > > > Signed-off-by: Will Deacon <will.dea...@arm.com> > > --- > > > > drivers/iommu/of_iommu.c | 14 ++++++++++++++ > > include/asm-generic/vmlinux.lds.h | 2 ++ > > include/linux/of_iommu.h | 21 +++++++++++++++++++++ > > 3 files changed, 37 insertions(+) > > I don't think this is the right direction. We've been preaching that > using initcall ordering is a bad thing and people should be using > deferred probe instead. Now we have a bunch of these OF tables that do > the exact opposite. Note that these are nothing more than a variant of > initcalls that get called at platform-specific points in time.
My idea to solve this problem was to defer probing of the bus master device from the add_device IOMMU operation. This obviously won't work with add_device called from the BUS_NOTIFY_ADD_DEVICE notifier, which led me to naively wonder whether we couldn't call the add_device operation from the BUS_NOTIFY_BIND_DRIVER notifier instead. > There are also ongoing discussions about how to change the device probe > order to use dependencies (such as phandles from device tree) to prevent > excessive deferred probing. With that in place this would be solved in a > much more generic way. -- Regards, Laurent Pinchart
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