Re: [Xen-devel] [PATCH v2 12/12] xen/iommu: smmu: Add Xen specific code to be able to use the driver

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 27/01/15 16:46, Stefano Stabellini wrote:
> On Fri, 16 Jan 2015, Julien Grall wrote:
>> The main goal is to modify as little the Linux code to be able to port
>> easily new feature added in Linux repo for the driver.
> 
> Agreed.
> 
> 
>> To achieve that we:
>>     - Add helpers to Linux function not implemented on Xen
> 
> Good idea, I would take it further and move the helpers to a separate
> file that smmu.c #includes. Or it could work the other way around: you
> could move the original code to smmu-linux.c that get #included into
> smmu.c

We would have to modify smmu-linux.c for disabling some functions and/or
modify them.

Although for the later, there is only a couple functions modified.

> 
>>     - Add callbacks used by Xen to do our own stuff and call Linux ones
>>     - Only modify when required the code which comes from Linux. If so a
>>     comment has been added with /* Xen: ... */ explaining why it's
>>     necessary.
> 
> I wonder if it makes sense to keep your changes in patch format and
> apply the patch at run time as part of the make system.
> 
> Of course you would need to be careful to keep the patched smmu.c
> separate from the original, otherwise it would get very confusing when
> people works on their changes.

IHMO, it makes more difficult to review and work with it. Although it
may be easier for porting change from Linux in the future.

Regards,

-- 
Julien Grall

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