Re: [PATCH 1/1] iova: Allow compiling the library without IOMMU support

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

On Thu, Jan 03, 2019 at 12:52:00AM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> Thank you for the patch.
> 
> On Wednesday, 2 January 2019 23:16:57 EET Sakari Ailus wrote:
> > Drivers such as the Intel IPU3 ImgU driver use the IOVA library to manage
> > the device's own virtual address space while not implementing the IOMMU
> > API.
> 
> Why is that ? Could the IPU3 IOMMU be implemented as an IOMMU driver ?

You could do that, but:

- it's a single PCI device so there's no advantage in doing so and

- doing that would render the device inoperable if an IOMMU is enabled in
  the system, as chaining IOMMUs is not supported in the IOMMU framework
  AFAIK.

> 
> > Currently the IOVA library is only compiled if the IOMMU support is
> > enabled, resulting into a failure during linking due to missing symbols.
> > 
> > Fix this by defining IOVA library Kconfig bits independently of IOMMU
> > support configuration, and descending to the iommu directory
> > unconditionally during the build.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> >  drivers/Makefile      | 2 +-
> >  drivers/iommu/Kconfig | 7 ++++---
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/Makefile b/drivers/Makefile
> > index 578f469f72fb..d9c469983592 100644
> > --- a/drivers/Makefile
> > +++ b/drivers/Makefile
> > @@ -56,7 +56,7 @@ obj-y				+= tty/
> >  obj-y				+= char/
> > 
> >  # iommu/ comes before gpu as gpu are using iommu controllers
> > -obj-$(CONFIG_IOMMU_SUPPORT)	+= iommu/
> > +obj-y				+= iommu/
> > 
> >  # gpu/ comes after char for AGP vs DRM startup and after iommu
> >  obj-y				+= gpu/
> > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > index d9a25715650e..d2c83e62873d 100644
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -1,3 +1,7 @@
> > +# The IOVA library may also be used by non-IOMMU_API users
> > +config IOMMU_IOVA
> > +	tristate
> > +
> >  # IOMMU_API always gets selected by whoever wants it.
> >  config IOMMU_API
> >  	bool
> > @@ -81,9 +85,6 @@ config IOMMU_DEFAULT_PASSTHROUGH
> > 
> >  	  If unsure, say N here.
> > 
> > -config IOMMU_IOVA
> > -	tristate
> > -
> >  config OF_IOMMU
> >         def_bool y
> >         depends on OF && IOMMU_API
> 
> 
> -- 
> Regards,
> 
> Laurent Pinchart
> 
> 
> 

-- 
Sakari Ailus
sakari.ailus@linux.intel.com