Re: [PATCH v3 09/20] xen/dom0less: abstract Arm-specific p2m type name for device MMIO mappings

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 8/4/25 4:11 PM, Jan Beulich wrote:

> On 31.07.2025 17:58, Oleksii Kurochko wrote:
> > Rename `p2m_mmio_direct_dev` to a more architecture-neutral alias
> > `p2m_mmio_direct` to avoid leaking Arm-specific naming into common Xen code,
> > such as dom0less passthrough property handling.
> >
> > This helps reduce platform-specific terminology in shared logic and
> > improves clarity for future non-Arm ports (e.g. RISC-V or PowerPC).
> >
> > No functional changes — the definition is preserved via a macro alias
> > for Arm.
> >
> > Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
> >       
> I'm sorry, but no, ...
>
> > --- a/xen/arch/arm/include/asm/p2m.h
> > +++ b/xen/arch/arm/include/asm/p2m.h
> > @@ -137,6 +137,8 @@ typedef enum {
> >      p2m_max_real_type,  /* Types after this won't be store in the p2m */
> >  } p2m_type_t;
> >  
> > +#define p2m_mmio_direct p2m_mmio_direct_dev
> >       
> ... this isn't what I suggested. When Arm has three p2m_mmio_direct_*,
> randomly aliasing one to p2m_mmio_direct is imo more likely to create
> confusion than to help things. Imo you want to introduce ...
>     
This is not randomly, this what Arm uses for device's node(s), which is going
to be passthroughed...
> > --- a/xen/common/device-tree/dom0less-build.c
> > +++ b/xen/common/device-tree/dom0less-build.c
> > @@ -185,7 +185,7 @@ static int __init handle_passthrough_prop(struct kernel_info *kinfo,
> >                                 gaddr_to_gfn(gstart),
> >                                 PFN_DOWN(size),
> >                                 maddr_to_mfn(mstart),
> > -                               p2m_mmio_direct_dev);
> > +                               p2m_mmio_direct);
> >       
> ... a per-arch inline function which returns the type to use here.
> The name of the function would want to properly reflect the purpose;
> my limited DT knowledge may make arch_dt_passthrough_p2m_type() an
> entirely wrong suggestion.
>     
... But make it even more generic by providing an inline function which
just return p2m_type_t would be really better.
~ Oleksii