Re: [XEN][PATCH] common/libfdt: optimize usage

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.11.2025 19:01, Grygorii Strashko wrote:
> From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> 
> Now all libfdt features are built-it unconditionally, but...
> 
> X86: The libfdt is used on x86 only to parse Hyperlaunch/dom0less Xen
> nodes, so full libfdt is not needed in this case and minimal, RO
> configuration can be used.
> 
> ARM - situation is more complicated:
> 1) ARM reads Host DT (fdt.c RO)
> 2) ARM reads passthrough DT (RO)
> 3) ARM generates dom0/hwdom DT from Host DT (there is a mix of WIP and SW 
> APIs)
> 4) ARM generates domU DT (there is a mix of WIP and SW APIs)
> 4) With EFI enabled - ARM needs RW API and fdt_empty_tree
> 5) With CONFIG_OVERLAY_DTB - ARM needs RW and fdt_overlay API

This goes too far, imo.

> --- /dev/null
> +++ b/xen/common/libfdt/Kconfig
> @@ -0,0 +1,14 @@
> +config LIBFDT_WIP
> +     bool
> +
> +config LIBFDT_SW
> +    bool
> +
> +config LIBFDT_RW
> +    bool
> +
> +config LIBFDT_EMPTY_TREE
> +    bool
> +
> +config LIBFDT_OVERLAY
> +    bool

Nit: Inconsistent indentation.

Also, how would one be to guess which of these may need selecting? What do
"WIP", "SW", and "RW" stand for? What exactly would "empty tree" mean? Yes,
you follow what the files are named under libfdt/, but that naming is
overly cryptic, too. The comments at the top of these files also don't
say anything helpful.

Jan