Re: [PATCH 2/2] xen/pci: Gate all MSI code in common code with CONFIG_HAS_PCI_MSI

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Apr 06, 2021 at 04:09:34PM +0100, Julien Grall wrote:
> 
> 
> On 06/04/2021 15:59, Roger Pau Monné wrote:
> > On Tue, Apr 06, 2021 at 03:30:01PM +0100, Julien Grall wrote:
> > > So I think we want to be able to compile out the code if not used. That
> > > said, I think providing stub would be better to avoid multiple #ifdef in 
> > > the
> > > same function.
> > 
> > I think providing stubs is the way to go, that should allow to remove
> > the unneeded code without having to explicitly drop MSI support. As
> > said before, I think it's fine to provide those unimplemented for Arm
> > ATM, can be filled later if there's more pressing PCI work to do
> > first.
> 
> We should remove unneeded and *avoid* allocation. Providing stub for
> existing functions will only address the first problem.
> 
> For the allocation (see alloc_pdev()) , we will need to move it in separate
> function and gate them to prevent the allocation.
> 
> It would be wrong to gate the code with #ifdef CONFIG_X86. So I think
> Rahul's idea to provide the new #ifdef is correct.

I think all this needs to be in the commit message then, because from
my reading of the current message it seems like MSI code is only
removed because MSI support is not implemented on Arm, rather than Arm
not requiring such strict tracking of MSI accesses and MSI interrupt
setup. Likely the naming of the option needs to be adjusted also
together with the reduction of it's scope to stuff that explicitly
needs to be removed in the preprocessor opposed to adding arch
specific stubs.

Thanks, Roger.