Re: [PATCH 0/4] iommu: Prevent oops in iommu_get() and while arch_iommu is in use

[Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>]

Laurent Pinchart wrote:
> Hi Sakari,

Hi Laurent,

> On Wednesday 30 March 2011 10:16:56 Sakari Ailus wrote:
>> Laurent Pinchart wrote:
>>> On Friday 25 March 2011 20:37:55 Ramirez Luna, Omar wrote:
>>>> On Fri, Mar 25, 2011 at 10:13 AM, Sakari Ailus wrote:
>>>>> Hi,
>>>>>
>>>>> This patchset is aimed to fix a problem in arch_iommu implementation
>>>>> references. When an actual arch_iommu implementation is not loaded
>>>>> while iommu_get() is being called results to a kernel oops, as well as
>>>>> removing an arch_iommu implementation which is in use.
>>>>
>>>> How about fixing the dependency instead? Right now iommu2 depends on
>>>> iommu because of the calls to
>>>> install_iommu_arch/uninstall_iommu_arch... we should change that
>>>> dependency to iommu depend on iommu2. Something like iommu (plat)
>>>> querying iommu2 (mach) for devices to install.
>>>
>>> The reason why iommu depends on iommu2 and not the other way around is
>>> because several mach-specific iommu implementations should be able to
>>> coexist in the same kernel. The right one should be loaded at runtime.
>>>
>>> I think that Sakari's patches correcty fix the problems he noticed.
>>> However, they won't fix one basic issue, which is that the iommu2 module
>>> won't be automatically pulled in when the omap3isp module is loaded. The
>>> omap3isp driver will then fail to probe the device. That's better than
>>> crashing though.
>>
>> One option would be to specify the name of the module in the platform
>> data and request_module() that in omap_iommu_probe(). This would solve
>> the issue, not sure how pretty is this though.
> 
> Do we need that ? My understanding is that a machine will need a single mach-
> specific iommu implementation only. Drivers shouldn't need to care about that. 

Well, no more than that there would have to be a driver for the IOMMU
for that very hardware.

> The iommu implementation should be automatically selected based on the machine 
> time.

Machine type?

I agree, but where is the selection made?

-- 
Sakari Ailus
sakari.ailus@maxwell.research.nokia.com