Hi Robin/Lorenzo,

Hi Robin,Lorenzo,

quoted

On Wed, Nov 30, 2016 at 04:42:27PM +0000, Robin Murphy wrote:

quoted

On 30/11/16 16:17, Lorenzo Pieralisi wrote:

quoted

Sricharan, Robin,

I gave this series a go on ACPI and apart from an SMMU v3 fix-up
it seems to work, more thorough testing required though.

A key question below.

On Wed, Nov 30, 2016 at 05:52:16AM +0530, Sricharan R wrote:

quoted

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).

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/of_iommu.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index ee49081..349bd1d 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c

@@ -104,12 +104,20 @@ int of_get_dma_window(struct device_node *dn, const char *prefix, int index,
 	int err;

 	ops = iommu_get_instance(fwnode);
-	if (!ops || !ops->of_xlate)
+	if ((ops && !ops->of_xlate) ||
+	    (!ops && !of_match_node(&__iommu_of_table, iommu_spec->np)))

IIUC of_match_node() here is there to check there is a driver compiled
in for this device_node (aka compatible string in OF world), correct ?

Yes - specifically, it's checking the magic table for a matching
IOMMU_OF_DECLARE entry.

quoted

If that's the case (and I think that's what Sricharan was referring to
in his ACPI query) I need to cook-up something on the ACPI side to
emulate the OF linker table behaviour (or anyway to detect a driver is
actually in the kernel), it is not that difficult but it is key to know,
I will give it some thought to make it as clean as possible.

I didn't think this would be a concern for ACPI, since IORT works much
the same way the current of_iommu_init_fn/of_platform_device_create()
bodges in drivers so for DT. If you can only discover SMMUs from IORT,
then iort_init_platform_devices() will have already created every SMMU
that's going to exist before discovering other devices from wherever
they come from, thus you could never get into the situation of probing a
device without its SMMU being ready (if it's ever going to be). Is that
not right?

It is right, my point and question is: we are probing a device and we
have to know whether it is worth deferring its IOMMU DMA setup. On DT,
through of_match_node(&__iommu_of_table, iommu_device_node) we check at
once that:

1 - A device for the IOMMU exists

AND

2 - A driver for the IOMMU is compiled in the kernel

Is this correct ? As you said (1) is not a concern on ACPI IORT (because
we create the IOMMU device before _any_ other device so either the IOMMU
device is there or it will never be by the time master devices are
probed), but for (2) I need to slightly change how the IORT linker entry
work to make sure we can detect a driver is actually compiled in the
kernel, it is easy, I was just asking if my understanding was correct
and I think that was what Sricharan was referring to in his query.

Yes right, this was what i was looking for in the ACPI case and putting this
in the iort_iommu_xlate was needed to return EPROBE_DEFER when the
driver is not yet been probed.

With the thinking of taking this series through, would it be fine if i cleanup
the pci configure hanging outside and push it in to of/acpi_iommu configure
respectively ? This time with all neeeded for ACPI added as well.
 Also on the last post of V4, Lorenzo commented that it worked for him, although
still the of_match_node equivalent in ACPI has to be added. If i can get that,
then i will add that as well to make this complete.

Regards,
 Sricharan