On 14/02/2020 2:09 pm, John Garry wrote:
@@ -2420,6 +2421,10 @@ void pci_device_add(struct pci_dev *dev, struct
pci_bus *bus)
/* Set up MSI IRQ domain */
pci_set_msi_domain(dev);
+ parent = dev->dev.parent;
+ if (parent && parent->bus == &pci_bus_type)
+ device_link_add(&dev->dev, parent, DL_FLAG_AUTOPROBE_CONSUMER);
+
/* Notifier could use PCI capabilities */
dev->match_driver = false;
ret = device_add(&dev->dev);
--
This would work, but the problem is that if the port driver fails in
probing - and not just for -EPROBE_DEFER - then the child device will
never probe. This very thing happens on my dev board. However we could
expand the device links API to cover this sort of scenario.
Yes, that's an undesirable issue, but in fact I think it's mostly
indicative that involving drivers in something which is designed to
happen at a level below drivers is still fundamentally wrong and doomed
to be fragile at best.
Right, and even worse is that it relies on the port driver even existing
at all.
All this iommu group assignment should be taken outside device driver
probe paths.
However we could still consider device links for sync'ing the SMMU and
each device probing.
Yes, we should get that for DT now thanks to the of_devlink stuff, but
cooking up some equivalent for IORT might be worthwhile.
Another thought that crosses my mind is that when pci_device_group()
walks up to the point of ACS isolation and doesn't find an existing
group, it can still infer that everything it walked past *should* be put
in the same group it's then eventually going to return. Unfortunately I
can't see an obvious way for it to act on that knowledge, though, since
recursive iommu_probe_device() is unlikely to end well.
I'd be inclined not to change that code.
As for alternatives, it looks pretty difficult to me to disassociate the
group allocation from the dma_configure path.
Indeed it's non-trivial, but it really does need cleaning up at some
point.
Having just had yet another spark, does something like the untested
super-hack below work at all?
I tried it and it doesn't (yet) work.
Bleh - further reinforcement of the "ideas after 6PM are bad ideas" rule...
So when we try
iommu_bus_replay()->add_iommu_group()->iommu_probe_device()->arm_smmu_add_device(),
the iommu_fwspec is still NULL for that device - this is not set until
later when the device driver is going to finally probe in
iort_iommu_xlate()->iommu_fwspec_init(), and it's too late...
And this looks to be the reason for which current
iommu_bus_init()->bus_for_each_device(..., add_iommu_group) fails also.
Of course, just adding a 'correct' add_device replay without the
of_xlate process doesn't help at all. No wonder this looked suspiciously
simpler than where the first idea left off...
(on reflection, the core of this idea seems to be recycling the existing
iommu_bus_init walk rather than building up a separate "waiting list",
while forgetting that that wasn't the difficult part of the original
idea anyway)
On this current code mentioned, the principle of this seems wrong to me
- we call bus_for_each_device(..., add_iommu_group) for the first SMMU
in the system which probes, but we attempt to add_iommu_group() for all
devices on the bus, even though the SMMU for that device may yet to have
probed.
Yes, iommu_bus_init() is one of the places still holding a
deeply-ingrained assumption that the ops go live for all IOMMU instances
at once, which is what warranted the further replay in
of_iommu_configure() originally. Moving that out of
of_platform_device_create() to support probe deferral is where the
trouble really started.
Robin.
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