linux-kernel - Re: [PATCH v4 1/6] of: iommu: add ptr to OF node arg to of_iommu

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Date:	Fri, 30 Jan 2015 10:23:52 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:	Rob Herring <robherring2@...il.com>,
	Will Deacon <will.deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Joerg Roedel <joro@...tes.org>,
	Rob Herring <robh+dt@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH v4 1/6] of: iommu: add ptr to OF node arg to of_iommu_configure()

On 01/29/2015 07:24 PM, Laurent Pinchart wrote:
> Hi Rob,
>
> On Thursday 29 January 2015 10:49:38 Rob Herring wrote:
>> On Wed, Jan 28, 2015 at 5:32 PM, Laurent Pinchart wrote:
>>> 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.
>>
>> [...]
>>
>>>>> 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@...asonboard.com>
>>>
>>> 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.
>>
>> It was more confusing having np and node within the function.
>
> Agreed.
>
> How about master_np or iommu_master_np ? The latter might be a bit long.
>
Probabaly master_np suffice as this function is named 
of_iommu_configure(). I will update it.

-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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