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

[Robin Murphy]

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 <robin.murphy at 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 at 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.

> 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?

Robin.

> 
> Thanks,
> Lorenzo
> 
>>  		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 +194,34 @@ 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;
>>  }
>> -- 
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>>