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Subject[PATCH V11 02/11] iommu/of: Prepare for deferred IOMMU configuration
Date
From: Robin Murphy <robin.murphy@arm.com>

IOMMU configuration represents unchanging properties of the hardware,
and as such should only need happen once in a device's lifetime, but
the necessary interaction with the IOMMU device and driver complicates
exactly when that point should be.

Since the only reasonable tool available for handling the inter-device
dependency is probe deferral, we need to prepare of_iommu_configure()
to run later than it is currently called (i.e. at driver probe rather
than device creation), to handle being retried, and to tell whether a
not-yet present IOMMU should be waited for or skipped (by virtue of
having declared a built-in driver or not).

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
drivers/iommu/of_iommu.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index 8f4e599..c8be889 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -96,6 +96,19 @@ int of_get_dma_window(struct device_node *dn, const char *prefix, int index,
}
EXPORT_SYMBOL_GPL(of_get_dma_window);

+static bool of_iommu_driver_present(struct device_node *np)
+{
+ /*
+ * If the IOMMU still isn't ready by the time we reach init, assume
+ * it never will be. We don't want to defer indefinitely, nor attempt
+ * to dereference __iommu_of_table after it's been freed.
+ */
+ if (system_state > SYSTEM_BOOTING)
+ return false;
+
+ return of_match_node(&__iommu_of_table, np);
+}
+
static const struct iommu_ops
*of_iommu_xlate(struct device *dev, struct of_phandle_args *iommu_spec)
{
@@ -104,12 +117,20 @@ int of_get_dma_window(struct device_node *dn, const char *prefix, int index,
int err;

ops = iommu_ops_from_fwnode(fwnode);
- if (!ops || !ops->of_xlate)
+ if ((ops && !ops->of_xlate) ||
+ (!ops && !of_iommu_driver_present(iommu_spec->np)))
return NULL;

err = iommu_fwspec_init(dev, &iommu_spec->np->fwnode, ops);
if (err)
return ERR_PTR(err);
+ /*
+ * The otherwise-empty fwspec handily serves to indicate the specific
+ * IOMMU device we're waiting for, which will be useful if we ever get
+ * a proper probe-ordering dependency mechanism in future.
+ */
+ if (!ops)
+ return ERR_PTR(-EPROBE_DEFER);

err = ops->of_xlate(dev, iommu_spec);
if (err)
@@ -186,14 +207,34 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
struct device_node *master_np)
{
const struct iommu_ops *ops;
+ struct iommu_fwspec *fwspec = dev->iommu_fwspec;

if (!master_np)
return NULL;

+ if (fwspec) {
+ if (fwspec->ops)
+ return fwspec->ops;
+
+ /* In the deferred case, start again from scratch */
+ iommu_fwspec_free(dev);
+ }
+
if (dev_is_pci(dev))
ops = of_pci_iommu_init(to_pci_dev(dev), master_np);
else
ops = of_platform_iommu_init(dev, master_np);
+ /*
+ * If we have reason to believe the IOMMU driver missed the initial
+ * add_device callback for dev, replay it to get things in order.
+ */
+ if (!IS_ERR_OR_NULL(ops) && ops->add_device &&
+ dev->bus && !dev->iommu_group) {
+ int err = ops->add_device(dev);
+
+ if (err)
+ ops = ERR_PTR(err);
+ }

return IS_ERR(ops) ? NULL : ops;
}
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
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