Re: [PATCH 36/37] xen/arm: Provide Kconfig options for Arm to enable NUMA

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 24 Sep 2021, Wei Chen wrote:
> Hi Stefano,
> 
> On 2021/9/24 11:31, Stefano Stabellini wrote:
> > On Thu, 23 Sep 2021, Wei Chen wrote:
> > > Arm platforms support both ACPI and device tree. We don't
> > > want users to select device tree NUMA or ACPI NUMA manually.
> > > We hope usrs can just enable NUMA for Arm, and device tree
> >            ^ users
> > 
> > > NUMA and ACPI NUMA can be selected depends on device tree
> > > feature and ACPI feature status automatically. In this case,
> > > these two kinds of NUMA support code can be co-exist in one
> > > Xen binary. Xen can check feature flags to decide using
> > > device tree or ACPI as NUMA based firmware.
> > > 
> > > So in this patch, we introduce a generic option:
> > > CONFIG_ARM_NUMA for user to enable NUMA for Arm.
> >                        ^ users
> > 
> 
> OK
> 
> > > And one CONFIG_DEVICE_TREE_NUMA option for ARM_NUMA
> > > to select when HAS_DEVICE_TREE option is enabled.
> > > Once when ACPI NUMA for Arm is supported, ACPI_NUMA
> > > can be selected here too.
> > > 
> > > Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> > > ---
> > >   xen/arch/arm/Kconfig | 11 +++++++++++
> > >   1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> > > index 865ad83a89..ded94ebd37 100644
> > > --- a/xen/arch/arm/Kconfig
> > > +++ b/xen/arch/arm/Kconfig
> > > @@ -34,6 +34,17 @@ config ACPI
> > >             Advanced Configuration and Power Interface (ACPI) support for 
> > > Xen is
> > >             an alternative to device tree on ARM64.
> > >   + config DEVICE_TREE_NUMA
> > > + def_bool n
> > > + select NUMA
> > > +
> > > +config ARM_NUMA
> > > + bool "Arm NUMA (Non-Uniform Memory Access) Support (UNSUPPORTED)" if
> > > UNSUPPORTED
> > > + select DEVICE_TREE_NUMA if HAS_DEVICE_TREE
> > 
> > Should it be: depends on HAS_DEVICE_TREE ?
> > (And eventually depends on HAS_DEVICE_TREE || ACPI)
> > 
> 
> As the discussion in RFC [1]. We want to make ARM_NUMA as a generic
> option can be selected by users. And depends on has_device_tree
> or ACPI to select DEVICE_TREE_NUMA or ACPI_NUMA.
> 
> If we add HAS_DEVICE_TREE || ACPI as dependencies for ARM_NUMA,
> does it become a loop dependency?
> 
> https://lists.xenproject.org/archives/html/xen-devel/2021-08/msg00888.html

OK, I am fine with that. I was just trying to catch the case where a
user selects "ARM_NUMA" but actually neither ACPI nor HAS_DEVICE_TREE
are selected so nothing happens. I was trying to make it clear that
ARM_NUMA depends on having at least one between HAS_DEVICE_TREE or ACPI
because otherwise it is not going to work.

That said, I don't think this is important because HAS_DEVICE_TREE
cannot be unselected. So if we cannot find a way to express the
dependency, I think it is fine to keep the patch as is.