linux-kernel - Re: [PATCH 10/29] drivers: add DRIVER_HAS_OWN_IOMMU

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Message-id: <54046186.5030407@samsung.com>
Date:	Mon, 01 Sep 2014 14:07:34 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Thierry Reding <treding@...dia.com>,
	Rob Herring <robh@...nel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Shaik Ameer Basha <shaik.ameer@...sung.com>,
	Inki Dae <inki.dae@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Joerg Roedel <joro@...tes.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Cho KyongHo <pullip.cho@...sung.com>
Subject: Re: [PATCH 10/29] drivers: add DRIVER_HAS_OWN_IOMMU_MANAGER flag

Hello,

On 2014-09-01 13:56, Arnd Bergmann wrote:
> On Monday 01 September 2014 12:47:08 Marek Szyprowski wrote:
>>> Who do you think needs to set this flag, and who needs to read it?
>> In the proposed solution Exynos IOMMU driver creates a separate IO
>> address space
>> for every client device in a system and binds it to the default
>> dma-mapping space
>> for the given device. When drivers are doing its own management of IO
>> address
>> space, instead of relying on what is available by default with dma-mapping
>> interface, this will require releasing of the previously created default
>> structures and resources. So this flag is set by the driver doing its own
>> management of io address space. The flags is then checked by Exynos
>> IOMMU driver
>> to avoid creating the default dma-mapping address space for devices
>> which driver
>> does its own management.
> I don't completely understand it yet. I would assume the device
> to be added to the default domain at device creation time
> (of_platform_populate), way before we know which device driver
> is going to be used. How can this prevent the iommu driver
> from doing the association with the domain?

of_platform_populate() is too early to do the association, because that 
time the
exynos iommu driver is even not yet probed.

The association with default dma-mapping domain is done in
IOMMU_GROUP_NOTIFY_BIND_DRIVER notifier, just before binding the driver 
to the
given device. This way iommu driver can check dev->driver->flags and 
skip creating
default dma-mapping domain if driver announces that it wants to handle it by
itself.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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