Re: [PATCH v3 5/9] iommu/of: Handle iommu-map property for PCI

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 01/07/16 11:31, Will Deacon wrote:
> On Tue, Jun 28, 2016 at 04:48:24PM +0100, Robin Murphy wrote:
>> Now that we have a way to pick up the RID translation and target IOMMU,
>> hook up of_iommu_configure() to bring PCI devices into the of_xlate
>> mechanism and allow them IOMMU-backed DMA ops without the need for
>> driver-specific handling.
>>
>> Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
>> ---
>>
>> v3: Use explicit "iommu-map-mask", drop of_device_is_available() check.
>>
>>  drivers/iommu/of_iommu.c | 43 ++++++++++++++++++++++++++++++++++++-------
>>  1 file changed, 36 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
>> index 7e6369cffc95..25406a8b9d4e 100644
>> --- a/drivers/iommu/of_iommu.c
>> +++ b/drivers/iommu/of_iommu.c
>> @@ -22,6 +22,7 @@
>>  #include <linux/limits.h>
>>  #include <linux/of.h>
>>  #include <linux/of_iommu.h>
>> +#include <linux/of_pci.h>
>>  #include <linux/of_platform.h>
>>  #include <linux/slab.h>
>>  
>> @@ -138,20 +139,48 @@ const struct iommu_ops *of_iommu_get_ops(struct device_node *np)
>>  	return ops;
>>  }
>>  
>> +static int __get_pci_rid(struct pci_dev *pdev, u16 alias, void *data)
>> +{
>> +	struct of_phandle_args *iommu_spec = data;
>> +
>> +	iommu_spec->args[0] = alias;
>> +	return iommu_spec->np == pdev->bus->dev.of_node;
>> +}
>> +
>>  const struct iommu_ops *of_iommu_configure(struct device *dev,
>>  					   struct device_node *master_np)
>>  {
>>  	struct of_phandle_args iommu_spec;
>> -	struct device_node *np;
>> +	struct device_node *np = NULL;
> 
> This sets off some alarm bells...
> 
>>  	const struct iommu_ops *ops = NULL;
>>  	int idx = 0;
>>  
>> -	/*
>> -	 * We can't do much for PCI devices without knowing how
>> -	 * device IDs are wired up from the PCI bus to the IOMMU.
>> -	 */
>> -	if (dev_is_pci(dev))
>> -		return NULL;
>> +	if (dev_is_pci(dev)) {
>> +		/*
>> +		 * Start by tracing the RID alias down the PCI topology as
>> +		 * far as the host bridge whose OF node we have...
>> +		 */
>> +		iommu_spec.np = master_np;
>> +		pci_for_each_dma_alias(to_pci_dev(dev), __get_pci_rid,
>> +				       &iommu_spec);
>> +		/*
>> +		 * ...then find out what that becomes once it escapes the PCI
>> +		 * bus into the system beyond, and which IOMMU it ends up at.
>> +		 */
>> +		if (of_pci_map_rid(master_np, iommu_spec.args[0], "iommu-map",
>> +				    "iommu-map-mask", &np, iommu_spec.args))
>> +			return NULL;
> 
> ... because you're assumedly initialising np to NULL in case of_pci_map_rid
> returns 0, but doesn't set np...

Not quite; we're passing &np as the optional "target" argument to
of_pci_map_rid - since that argument is provided, it will either find a
matching translation (and fill in np in the process) or return -EFAULT.

>> +
>> +		/* We're not attempting to handle multi-alias devices yet */
>> +		iommu_spec.np = np;
>> +		iommu_spec.args_count = 1;
>> +		ops = of_iommu_get_ops(np);
> 
> ... and then we call of_iommu_get_ops(NULL). Does that make any sense?

It would actually work out, since nobody should have registered any ops
for a NULL node, but as above won't happen in practice anyway.

Robin.

> 
> Will
>