Re: [PATCH 1/2] iommu/omap: Reverse dependency between omap-iommu and omap-iommu2

[Suman Anna <s-anna@ti.com>]

Hi Laurent,

> On Tuesday 09 September 2014 16:33:11 Suman Anna wrote:
>> On 09/09/2014 10:45 AM, Laurent Pinchart wrote:
>>> The OMAP IOMMU driver supports both the OMAP1 and OMAP2+ IOMMU variants
>>> by splitting the driver into a core module and a thin arch-specific
>>> operations module.
>>>
>>> (In practice only the OMAP2+ module omap-iommu2 is implemented, but
>>> let's not denigrate the effort.)
>>
>> Thank you for the patch. I had something similar in my list of cleanup
>> TODO items on the OMAP IOMMU driver, but I was intending to cut down
>> more and consolidate the omap-iommu.c and omap-iommu2.c files into a
>> single one.
>>
>> This had been the case from the introduction of the driver going back to
>> v2.6.30, and OMAP1 was never added and I doubt it would be added anytime
>> in the foreseeable future.
>>
>>> The arch-specific operations module registers itself with the OMAP IOMMU
>>> core module at initialization time. This initializes a module global
>>> arch-specific operations pointer, used at runtime by the IOMMU
>>> instances.
>>>
>>> This scheme causes several issues. In addition to making it impossible
>>> to support different OMAP IOMMU types in a single system (which in all
>>> fairness is quite unlikely to happen),
>>
>> Yep, except for a few enhancements (like reporting Fault PC address on
>> OMAP4 DSPs, and dropping both endianness support), the core IOMMU
>> functionality hasn't changed much between OMAP2 and the latest OMAP4+
>> SoCs. So, my plan was to completely get rid of the iommu_functions (it
>> also eliminates the need for exporting most of the OMAP IOMMU API). So
>> while I am ok with the current patch, I prefer consolidation than
>> keeping the scalability alive, it can always be added if a need for that
>> arises. What do you think?
> 
> I agree with your approach, but in the meantime we have a problem to solve. 
> How about applying this patch now (it goes in the right direction anyway), and 
> then removing the iommu functions when you will have time ?

Can you give the subsys_initcall solution a try to see if that resolves
the problem at hand? That would be a much smaller change, if that
doesn't work we can go with this patch.

I will work on my cleanup list for 3.19.

regards
Suman

> 
>>  it also causes initialization
>>
>>> ordering issues by requiring the arch-specific operations module to be
>>> loaded before any IOMMU user. This results in a probe breakage with the
>>> OMAP3 ISP driver when not compiled as a module.
>>
>> This can be fixed if we make the current omap-iommu2.c as a
>> subsys_initcall as well, right?
>>
>> regards
>> Suman
>>
>>> Fix the problem by inverting the dependency. Instead of having the
>>> omap-iommu2 module register itself to iommu-omap, make the iommu-omap
>>> retrieve the omap-iommu2 operations structure directly when probing the
>>> IOMMU device. This ensures that a probed IOMMU will always have valid
>>> arch-specific operations.
>>>
>>> As the arch-specific operations pointer is now initialized at probe
>>> time, this change requires turning it from a global variable into a
>>> per-device variable.
>>>
>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>> ---
>>>
>>>  drivers/iommu/omap-iommu-debug.c |  6 ++-
>>>  drivers/iommu/omap-iommu.c       | 94 +++++++++++++----------------------
>>>  drivers/iommu/omap-iommu.h       | 10 ++++-
>>>  drivers/iommu/omap-iommu2.c      | 18 +-------
>>>  4 files changed, 45 insertions(+), 83 deletions(-)
>