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

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Date:	Mon, 1 Sep 2014 09:07:49 +0200
From:	Thierry Reding <treding@...dia.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Shaik Ameer Basha" <shaik.ameer@...sung.com>,
	Cho KyongHo <pullip.cho@...sung.com>,
	"Joerg Roedel" <joro@...tes.org>, Olof Johansson <olof@...om.net>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Rob Herring <robh@...nel.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Inki Dae <inki.dae@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	"Tomasz Figa" <tomasz.figa@...il.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH 10/29] drivers: add DRIVER_HAS_OWN_IOMMU_MANAGER flag

On Mon, Sep 01, 2014 at 07:22:32AM +0200, Marek Szyprowski wrote:
> Hi Greg,
> 
> On 2014-08-05 12:47, Marek Szyprowski wrote:
> > This patch adds a new flags for device drivers. This flag instructs
> > kernel that the device driver does it own management of IOMMU assisted
> > IO address space translations, so no default dma-mapping structures
> > should be initialized.
> >
> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > ---
> >   include/linux/device.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 5f4ff02..2e62371 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -253,6 +253,8 @@ struct device_driver {
> >   
> >   /* disables bind/unbind via sysfs */
> >   #define DRIVER_SUPPRESS_BIND_ATTRS	(1 << 0)
> > +/* driver uses own methods to manage IO address space */
> > +#define DRIVER_HAS_OWN_IOMMU_MANAGER	(1 << 1)
> >   
> >   extern int __must_check driver_register(struct device_driver *drv);
> >   extern void driver_unregister(struct device_driver *drv);
> 
> Could you comment if the approach of using flags in the struct driver
> could be accepted? I've converted suppress_bind_attrs entry to flags to
> avoid extending the structure, please see patch "[PATCH 05/29] drivers:
> convert suppress_bind_attrs parameter into flags".

Is this really necessary? What I did as part of an RFC series for Tegra
IOMMU support is keep this knowledge within the IOMMU driver rather than
export it to the driver core.

The idea being that the IOMMU driver wouldn't create an ARM DMA/IOMMU
mapping by default but rather allow individual drivers to be marked as
"kernel-internal" and use the DMA/IOMMU glue in that case. Drivers such
as DRM would use the IOMMU API directly.

Thierry

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