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

[Ian Campbell <ian.campbell@citrix.com>]

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@citrix.com> wrote:
> > On Thu, 2015-03-19 at 20:07 +0530, vijay.kilari@gmail.com wrote:
> >> From: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
> >>
> >> 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.

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

Ian.