On 12/10/18 20:41, Bjorn Helgaas wrote:
s/iommu/IOMMU/ in subject
On Fri, Oct 12, 2018 at 03:59:13PM +0100, Jean-Philippe Brucker wrote:
Using the iommu-map binding, endpoints in a given PCI domain can be
managed by different IOMMUs. Some virtual machines may allow a subset of
endpoints to bypass the IOMMU. In some case the IOMMU itself is presented
s/case/cases/
as a PCI endpoint (e.g. AMD IOMMU and virtio-iommu). Currently, when a
PCI root complex has an iommu-map property, the driver requires all
endpoints to be described by the property. Allow the iommu-map property to
have gaps.
I'm not an IOMMU or virtio expert, so it's not obvious to me why it is
safe to allow devices to bypass the IOMMU. Does this mean a typo in
iommu-map could inadvertently allow devices to bypass it? Should we
indicate something in dmesg (and/or sysfs) about devices that bypass
it?
It's not really "allow devices to bypass the IOMMU" so much as "allow DT
to describe devices which the IOMMU doesn't translate". It's a bit of an
edge case for not-really-PCI devices, but FWIW I can certainly think of
several ways to build real hardware like that. As for inadvertent errors
leaving out IDs which *should* be in the map, that really depends on the
IOMMU/driver implementation - e.g. SMMUv2 with arm-smmu.disable_bypass=0
would treat the device as untranslated, whereas SMMUv3 would always
generate a fault upon any transaction due to no valid stream table entry
being programmed (not even a bypass one).
I reckon it's a sufficiently unusual case that keeping some sort of
message probably is worthwhile (at pr_info rather than pr_err) in case
someone does hit it by mistake.
Relaxing of_pci_map_rid also allows the msi-map property to have gaps,
At worst, I suppose we could always add yet another parameter for each
caller to choose whether a missing entry is considered an error or not.
Robin.
s/of_pci_map_rid/of_pci_map_rid()/
which is invalid since MSIs always reach an MSI controller. Thankfully
Linux will error out later, when attempting to find an MSI domain for the
device.
Not clear to me what "error out" means here. In a userspace program,
I would infer that the program exits with an error message, but I
doubt you mean that Linux exits.
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
---
drivers/pci/of.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 1836b8ddf292..2f5015bdb256 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -451,9 +451,10 @@ int of_pci_map_rid(struct device_node *np, u32 rid,
return 0;
}
- pr_err("%pOF: Invalid %s translation - no match for rid 0x%x on %pOF\n",
- np, map_name, rid, target && *target ? *target : NULL);
- return -EFAULT;
+ /* Bypasses translation */
+ if (id_out)
+ *id_out = rid;
+ return 0;
}
#if IS_ENABLED(CONFIG_OF_IRQ)
--
2.19.1
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