linux-kernel - Re: [PATCH 08/10] iommu/omap: Use bus_set_iommu instead of register

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Date:	Mon, 26 Sep 2011 14:22:14 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alex Williamson <alex.williamson@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	David Brown <davidb@...eaurora.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/10] iommu/omap: Use bus_set_iommu instead of
 register_iommu

On Mon, Sep 26, 2011 at 03:09:58AM -0400, Ohad Ben-Cohen wrote:
> On Fri, Sep 23, 2011 at 6:45 PM, Joerg Roedel <joerg.roedel@....com> wrote:
> > -       register_iommu(&omap_iommu_ops);
> > +       bus_set_iommu(&platform_bus_type, &omap_iommu_ops);
> 
> I'm not sure it makes a lot of sense to bind the iommu ops to the platform bus.
> 
> Unlike the pci bus, the platform bus is not really a hardware bus:
> it's some kind of a catch-all pseudo bus which is mostly used to to
> describe a collection of autonomous peripherals on an SoC.
> 
> As a result, IOMMU users on an SoC might actually not belong to the
> platform bus.

That is interesting. What bus do these IOMMU users you talk about belong
to?
Is it a seperate bus that originates from a platform device? in that
case the situation sounds a little bit like with USB on x86. The usb
controlers are PCI devices and DMA handles are allocated using the
pci_dev of the controler and not the usb_device.

Regards,

	Joerg

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