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

[Aaron Sierra <asierra@xes-inc.com>]

----- Original Message -----
> From: "Sakari Ailus" <sakari.ailus@linux.intel.com>
> Sent: Thursday, January 3, 2019 2:11:27 PM

Hi Laurent and Sakari,

I don't have much else to offer here, but wanted to second Sakari's
use case below.

> 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

I also use the IOVA library for a PCI device (PCIe-VME bridge) that has
IOMMU features, but isn't a general purpose IOMMU. I am eagerly following
along.

-Aaron

> - 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>