Re: [PATCH v2] ppc/vof: Make nextprop behave more like Open Firmware

["Alexey Kardashevskiy" <aik@ozlabs.ru>]

On Tue, 1 Apr 2025, at 01:26, BALATON Zoltan wrote:
> The FDT does not normally store name properties but reconstructs it
> from path but each node in Open Firmware should at least have this
> property. This is correctly handled in getprop but nextprop should
> also return it even if not present as a property. This patch fixes
> that and also skips phandle which does not appear in Open Firmware
> and only added for internal use by VOF.
> 
> Explicit name properties are still allowed because they are needed
> e.g. on the root node that guests expect to have specific names as
> seen on real machines instead of being empty so sometimes the node
> name may need to be overriden.
> 
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
> I've tested this with pegasos2 but don't know how to test spapr.
> v2:
> Fixed a typo in commit message
> Simplified loop to get next property name
> 
> hw/ppc/vof.c | 51 ++++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 34 insertions(+), 17 deletions(-)
> 
> diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c
> index 09cb77de93..790d67c096 100644
> --- a/hw/ppc/vof.c
> +++ b/hw/ppc/vof.c
> @@ -353,34 +353,51 @@ static uint32_t vof_nextprop(const void *fdt, uint32_t phandle,
> {
>      int offset, nodeoff = fdt_node_offset_by_phandle(fdt, phandle);
>      char prev[OF_PROPNAME_LEN_MAX + 1];
> -    const char *tmp;
> +    const char *tmp = NULL;
> +    bool match = false;
>  
>      if (readstr(prevaddr, prev, sizeof(prev))) {
>          return PROM_ERROR;
>      }
> -
> -    fdt_for_each_property_offset(offset, fdt, nodeoff) {
> -        if (!fdt_getprop_by_offset(fdt, offset, &tmp, NULL)) {
> -            return 0;
> +    /*
> +     * "name" may or may not be present in fdt but we should still return it.

yeah we should, at least, to match "getprop". I also wonder if VOF does not add "name", then what would do so, do we really expect to see such properties anywhere? Because if not, then we do not need to skip it as we won't find it.

> +     * Do that first and then skip it if seen later. Also skip phandle which is

(a nit) appears to me that if handling of a missing "name" was done after the last property, the patch would look simpler, but not sure and do not insist.

> +     * an internal value we added in vof_build_dt but should not appear here.

I would not hide anything though, unless it breaks something. Thanks,

> +     */
> +    if (prev[0] == '\0') {
> +        tmp = "name";
> +    } else {
> +        if (strcmp(prev, "name") == 0) {
> +            prev[0] = '\0';
>          }
> -        if (prev[0] == '\0' || strcmp(prev, tmp) == 0) {
> -            if (prev[0] != '\0') {
> -                offset = fdt_next_property_offset(fdt, offset);
> -                if (offset < 0) {
> -                    return 0;
> -                }
> -            }
> +        fdt_for_each_property_offset(offset, fdt, nodeoff) {
>              if (!fdt_getprop_by_offset(fdt, offset, &tmp, NULL)) {
>                  return 0;
>              }
> -
> -            if (VOF_MEM_WRITE(nameaddr, tmp, strlen(tmp) + 1) != MEMTX_OK) {
> -                return PROM_ERROR;
> +            if (strcmp(tmp, "name") == 0 || strcmp(tmp, "phandle") == 0) {
> +                continue;
> +            }
> +            if (match) {
> +                break;
>              }
> -            return 1;
> +            if (strcmp(prev, tmp) == 0) {
> +                match = true;
> +                continue;
> +            }
> +            if (prev[0] == '\0') {
> +                break;
> +            }
> +        }
> +        if (offset < 0) {
> +            return 0;
>          }
>      }
> -
> +    if (tmp) {
> +        if (VOF_MEM_WRITE(nameaddr, tmp, strlen(tmp) + 1) != MEMTX_OK) {
> +            return PROM_ERROR;
> +        }
> +        return 1;
> +    }
>      return 0;
> }
>  
> -- 
> 2.41.3
> 
>