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

[Murali Karicheri]

On 01/28/2015 08:32 AM, Will Deacon wrote:
> 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@xxxxxxxxxx>
> > > > > > > > Cc: Grant Likely<grant.likely@xxxxxxxxxx>
> > > > > > > > Cc: Rob Herring<robh+dt@xxxxxxxxxx>
> > > > > > > > Cc: Bjorn Helgaas<bhelgaas@xxxxxxxxxx>
> > > > > > > > Cc: Will Deacon<will.deacon@xxxxxxx>
> > > > > > > > Cc: Russell King<linux@xxxxxxxxxxxxxxxx>
> > > > > > > > Cc: Arnd Bergmann<arnd@xxxxxxxx>
> > > > > > > > Cc: Suravee Suthikulpanit<Suravee.Suthikulpanit@xxxxxxx>
> > > > > > > >
> > > > > > > > Signed-off-by: Murali Karicheri<m-karicheri2@xxxxxx>
> > > > > > > > ---
> > > > > > > >
> > > > > > > >    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.
Laurent, Will,

I don't have an IOMMU hardware to do more work on this. My patch series 
has been on this list for long and it is also increasing in scope :(

I would suggest a follow up patch to this from someone (probably Will) 
and my patch goes as is with out further update. Hope this is reasonable.

Murali
> 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


--
Murali Karicheri
Linux Kernel, Texas Instruments
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/