Re: [Xen-devel] [RFC PATCH v2 06/22] xen/arm: its: Port ITS driver to xen

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Thu, Apr 2, 2015 at 2:55 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> On Thu, 2015-04-02 at 13:55 +0530, Vijay Kilari wrote:
>> On Wed, Apr 1, 2015 at 5:04 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
>> > On Thu, 2015-03-19 at 20:07 +0530, vijay.kilari@xxxxxxxxx wrote:
>> >> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>> >>
>> >> This patch just makes ITS driver taken from linux
>> >> compiles in xen environment.
>> >
>> > What is your intention wrt future updates to this driver?
>> >
>> > Are you intending to keep things in sync and import things from the
>> > Linux side (similar to the smmu drviers) or are you taking the Linux
>> > code as a starting point and intending that it then be maintained
>> > independently as a Xen driver from then on?
>>
>> Yes, I intend to keep things in sync with Linux driver.
>> I have kept most the code same as Linux side except removing unused code.
>
> There is a tonne of changes going on if that is your goal, in particular
> in this patch but also in some of the following refactoring patches.
> When this series is over it seems like the driver would bear very little
> resemblance to the Linux one.
>
> If you want to go this route then to aid in future synchronisation from
> Linux patches the goal should be to make the changes to the Linux code
> as minimal as possible, by defining shim functions and typedefs etc at
> the top of the file, e.g. as Julien has tried to do with the smmu
> driver.
>
> Unlike the smmu stuff, which has a reasonably small and well-defined
> interface to the kernel which can be easily shimmed between Xen and
> Linux it's not clear to me that this approach is workable for ITS, the
> Xen and Linux interrupt handling systems are rather different and ITS
> needs to be more tightly integrated with other bits of Xen, in
> particular the GIC drivers.

Yes, there is lot of unnecessary code for Xen in ITS driver which is
trimmed down. However the whatever functions that are used are retained,
So that changes made to Linux driver can be easily mapped to ITS driver.

IMO, We can create macros from debug prints, memory allocation & cache mgmt
apis, that only reduces changes we make.

>
> However if you think maintaining something which can be synchronised
> from Linux is viable and desirable then that's ok by me.

Regards
Vijay

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