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

[Murali Karicheri <m-karicheri2@ti.com>]

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@8bytes.org>
>>>>>>>> Cc: Grant Likely<grant.likely@linaro.org>
>>>>>>>> Cc: Rob Herring<robh+dt@kernel.org>
>>>>>>>> Cc: Bjorn Helgaas<bhelgaas@google.com>
>>>>>>>> Cc: Will Deacon<will.deacon@arm.com>
>>>>>>>> Cc: Russell King<linux@arm.linux.org.uk>
>>>>>>>> Cc: Arnd Bergmann<arnd@arndb.de>
>>>>>>>> Cc: Suravee Suthikulpanit<Suravee.Suthikulpanit@amd.com>
>>>>>>>>
>>>>>>>> Signed-off-by: Murali Karicheri<m-karicheri2@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.
>
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