Re: [PATCH v2 3/7] xen/common: Move Arm's bootfdt to common

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 19/12/2023 17:03, Jan Beulich wrote:
> On 15.12.2023 03:43, Shawn Anastasio wrote:
> > Move Arm's bootfdt.c to xen/common so that it can be used by other
> > device tree architectures like PPC and RISCV. Only a minor change to
> > conditionalize a call to a function only available on EFI-supporting
> > targets was made to the code itself.
> >
> > Suggested-by: Julien Grall <julien@xxxxxxx>
> > Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
> > ---
> >   xen/arch/arm/Makefile                          |  1 -
> >   xen/common/Makefile                            |  1 +
> >   xen/common/device-tree/Makefile                |  1 +
> >   xen/{arch/arm => common/device-tree}/bootfdt.c | 15 +++++++++------
> >   4 files changed, 11 insertions(+), 7 deletions(-)
> >   create mode 100644 xen/common/device-tree/Makefile
> >   rename xen/{arch/arm => common/device-tree}/bootfdt.c (98%)
> I think this wants to come with an update to ./MAINTAINERS, such that
> the file doesn't change maintainership.
>
> > --- a/xen/arch/arm/bootfdt.c
> > +++ b/xen/common/device-tree/bootfdt.c
> > @@ -431,12 +431,15 @@ static int __init early_scan_node(const void *fdt,
> >   {
> >       int rc = 0;
> >   
> > -    /*
> > -     * If Xen has been booted via UEFI, the memory banks are
> > -     * populated. So we should skip the parsing.
> > -     */
> > -    if ( !efi_enabled(EFI_BOOT) &&
> > -         device_tree_node_matches(fdt, node, "memory") )
> > +    if ( device_tree_node_matches(fdt, node, "memory") )
> > +#if defined(CONFIG_ARM_EFI)
> > +        /*
> > +         * If Xen has been booted via UEFI, the memory banks are
> > +         * populated. So we should skip the parsing.
> > +         */
> > +        if ( efi_enabled(EFI_BOOT) )
> > +            return rc;
> > +#endif
> I'm not a DT maintainer, but I don't like this kind of #ifdef, the more
> that maybe PPC and quite likely RISC-V are likely to also want to support
> EFI boot. But of course there may be something inherently Arm-specific
> here that I'm unaware of.
Right now, I can't think how this is Arm specific. If you are using 
UEFI, then you are expected to use the UEFI memory map rather than the 
content of the device-tree.
However, we don't have a CONFIG_EFI option. It would be nice to 
introduce one but I am not sure I would introduce it just for this #ifdef.
Cheers,

--
Julien Grall