Re: [Xen-devel] [RFC PATCH v1 2/7] iommu/arm: ipmmu-vmsa: Add Xen changes for main driver

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 23 Aug 2017, Julien Grall wrote:
> Hi Oleksandr,
> 
> On 21/08/17 16:53, Oleksandr Tyshchenko wrote:
> > On Thu, Aug 10, 2017 at 6:13 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > > On 10/08/17 15:27, Oleksandr Tyshchenko wrote:
> > > > I would like to clarify what need to be done from my side.
> > > > Should I wait for the missing things reach upsteam and then rebase on
> > > > the mainline driver?
> > > > Or should I rewrite this driver without following Linux?
> > > 
> > > 
> > > I don't have a clear answer here. As I said, we need to weight pros and
> > > cons
> > > to use Linux driver over our own.
> > > 
> > > At the moment, you are using a BSP driver which has more features but
> > > modified quite a lot. We don't even know when this is going to be merged
> > > in
> > > Linux.
> > > 
> > > Keeping code close to Linux requires some hacks that are acceptable if you
> > > can benefits from the community (bug fix, review...). As the driver is
> > > taken
> > > from the BSP, we don't know if the code will stay in the current form nor
> > > be
> > > able to get bug fix.
> > 
> > I got it. Completely agree with you.
> > But, we need to choose which direction we should follow. We have 3
> > options at the moment
> > and I am OK with each of them:
> > 1. direct port from BSP (current implementation).
> > 2. direct port from mainline Linux (when it has required support).
> > 3. new driver based on BSP/Linux and contains only relevant to Xen things.
> > 
> > I am starting to think that options 2 or 3 (+) would be more suitable.
> > What do you think?
> 
> The option 2 rely on the changes to be merged in Linux. If I understand
> correctly, we don't have any timeline for this.
> 
> So I would lean towards option 3 to get a support in Xen.
> 
> Stefano, do you have any opinion?

I agree with Julien. Option 3 is the way to go. There is only a benefit
in staying close to Linux if their driver is in good state, fully
featured, and well-maintained. And we certainly don't want to block your
work on waiting for somebody else who might or might nor merge his
changes in Linux. In this case, option 3 is best. I warn you, you might
have to maintain this driver in Xen going forward though :-)

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