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

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Date:	Thu, 29 Jan 2015 10:49:38 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Will Deacon <will.deacon@....com>,
	Murali Karicheri <m-karicheri2@...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 Wed, Jan 28, 2015 at 5:32 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> 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.

[...]

>> > 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.

Rob
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