[PATCH v4 1/6] of: iommu: add ptr to OF node arg to of_iommu_configure()

[Will Deacon]

On Wed, Jan 28, 2015 at 01:15:10PM +0000, Laurent Pinchart wrote:
> On Wednesday 28 January 2015 12:29:42 Will Deacon wrote:
> > On Wed, Jan 28, 2015 at 12:23:03PM +0000, Laurent Pinchart wrote:
> > > On Wednesday 28 January 2015 11:33:00 Will Deacon wrote:
> > >> On Mon, Jan 26, 2015 at 06:49:01PM +0000, Murali Karicheri wrote:
> > >>> On 01/25/2015 08:32 AM, Laurent Pinchart wrote:
> > >>>> On Friday 23 January 2015 17:32:34 Murali Karicheri wrote:
> > >>>>> Function of_iommu_configure() is called from of_dma_configure() to
> > >>>>> setup iommu ops using DT property. This API is currently used for
> > >>>>> platform devices for which DMA configuration (including iommu ops)
> > >>>>> may come from device's parent. To extend this functionality for PCI
> > >>>>> devices, this API need to take a parent node ptr as an argument
> > >>>>> instead of assuming device's parent. This is needed since for PCI,
> > >>>>> the dma configuration may be defined in the DT node of the root bus
> > >>>>> bridge's parent device. Currently only dma-range is used for PCI and
> > >>>>> iommu is not supported. So return error if the device is PCI.
> > >>>>> 
> > >>>>> Cc: Joerg Roedel<joro at 8bytes.org>
> > >>>>> Cc: Grant Likely<grant.likely at linaro.org>
> > >>>>> Cc: Rob Herring<robh+dt at kernel.org>
> > >>>>> Cc: Bjorn Helgaas<bhelgaas at google.com>
> > >>>>> Cc: Will Deacon<will.deacon at arm.com>
> > >>>>> Cc: Russell King<linux at arm.linux.org.uk>
> > >>>>> Cc: Arnd Bergmann<arnd at arndb.de>
> > >>>>> Cc: Suravee Suthikulpanit<Suravee.Suthikulpanit at amd.com>
> > >>>>> 
> > >>>>> Signed-off-by: Murali Karicheri<m-karicheri2 at ti.com>
> > >>>>> ---
> > >>>>> 
> > >>>>>   drivers/iommu/of_iommu.c |   10 ++++++++--
> > >>>>>   drivers/of/platform.c    |    2 +-
> > >>>>>   include/linux/of_iommu.h |    6 ++++--
> > >>>>>   3 files changed, 13 insertions(+), 5 deletions(-)
> > >>>>> 
> > >>>>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > >>>>> index af1dc6a..439235b 100644
> > >>>>> --- a/drivers/iommu/of_iommu.c
> > >>>>> +++ b/drivers/iommu/of_iommu.c
> > >>>>> @@ -133,19 +133,25 @@ struct iommu_ops *of_iommu_get_ops(struct
> > >>>>> device_node *np)
> > >>>>>   	return ops;
> > >>>>>  }
> > >>>>> 
> > >>>>> -struct iommu_ops *of_iommu_configure(struct device *dev)
> > >>>>> +struct iommu_ops *of_iommu_configure(struct device *dev,
> > >>>>> +				     struct device_node *iommu_np)
> > >>>>>  {
> > >>>>>   	struct of_phandle_args iommu_spec;
> > >>>>>   	struct device_node *np;
> > >>>>>   	struct iommu_ops *ops = NULL;
> > >>>>>   	int idx = 0;
> > >>>>> 
> > >>>>> +	if (dev_is_pci(dev)) {
> > >>>>> +		dev_err(dev, "iommu is currently not supported for PCI\n");
> > >>>>> +		return NULL;
> > >>>>> +	}
> > >>>>> +
> > >>>>>   	/*
> > >>>>>   	 * We don't currently walk up the tree looking for a parent
> > >>>>>   	 IOMMU.
> > >>>>>   	 * See the `Notes:' section of
> > >>>>>   	 * Documentation/devicetree/bindings/iommu/iommu.txt
> > >>>>>   	 */
> > >>>> 
> > >>>> Wouldn't it be better to fix this rather than passing the device node
> > >>>> pointer to the function ? The solution would be more generic.
> > >>> 
> > >>> Will Deacon (Copied here) is working on this as we alteady discussed
> > >>> in this thread. So it will be addressed by him in another series.
> > >> 
> > >> Well, "working on this" equates to "has it somewhere near the bottom of
> > >> a very long list" :)
> > > 
> > > What's your opinion on this patch then, do you think adding the iommu_np
> > > argument makes sense as a temporary hack, or should we instead walk up the
> > > tree looking for an iommus attribute in parent nodes ? I don't expect that
> > > to be insanely difficult to code.
> > 
> > If walking up the tree is useful, then I think we should do that and update
> > the Documentation to reflect the new behaviour.
> 
> If I understand Murali's patch set right (please correct me if that's not the 
> case) the PCI code walks up the DT nodes hierarchy to the parent node that 
> contains the iommus attribute and passes a pointer to that node to this 
> function. It's thus a PCI-specific solution. As a temporary hack that's OK I 
> suppose, but if implementing it right straight away isn't difficult that would 
> be better.

It looks to me like the code walks the PCI topology to get the DT node for
the host controller, and passes *that* to of_dma_configure. That sounds
like the right thing to do to me, especially since the PCI topology is
likely not encoded in the device-tree. So actually, it is passing the
first parent node afaict.

The part I'm more interested in is the mapping of RequesterID (PCI dma
alias) to IOMMU ID when we transition from the PCI topology to the DT
topology. Currently, it seems to be 1:1 on the platforms I have, but I
doubt this will always be the case.

Will