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

From: Murali Karicheri
Date: Thu Jan 29 2015 - 10:56:52 EST

On 01/28/2015 06:32 PM, Laurent Pinchart wrote:
Hi Will,

On Wednesday 28 January 2015 13:32:19 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.

Indeed, that's right. I forgot for a moment that we have non-DT devices ;-)

Acked-by: Laurent Pinchart<laurent.pinchart@xxxxxxxxxxxxxxxx>

Murali, nitpicking a bit, shouldn't the iommu_np parameter be renamed ? It
points to the node containing the iommus parameter, not to the iommu node, so
the current name is slightly confusing. A brief kerneldoc above the function
would also help. This can be the subject of a separate patch.
Probably the doc part can be added by Will. The iommu_np was a suggestion from Rob, if I recollect. Isn't the iommu_np points to the iommu device, and if so, iommu_np make sense.

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.



--
Murali Karicheri
Linux Kernel, Texas Instruments
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