Subject: [PATCH 02/10] iommu/of: Prepare for deferred IOMMU configuration

From: [email-masked] (Sricharan)
Date: Thu, 5 Jan 2017 14:04:37 +0530

Hi Robin/Lorenzo,

>Hi Robin,Lorenzo,
>
>>On Wed, Nov 30, 2016 at 04:42:27PM +0000, Robin Murphy wrote:
>>> On 30/11/16 16:17, Lorenzo Pieralisi wrote:
>>> > 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:
>>> >> From: Robin Murphy <[email-masked]>
>>> >>
>>> >> 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 <[email-masked]>
>>> >> ---
>>> >>  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.
>>>
>>> > 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