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 02:24:51 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Rob Herring <robherring2@...il.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()

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.

-- 
Regards,

Laurent Pinchart

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