[External] Re: [PATCH v3 2/3] riscv: cacheinfo: initialize cacheinfo's level and type from ACPI PPTT

[yunhui cui]

Hi Jeremy,

On Wed, Apr 17, 2024 at 4:04 AM Jeremy Linton <jeremy.linton at arm.com> wrote:
>
> Hi,
>
>
> On 4/15/24 22:14, Yunhui Cui wrote:
> > Before cacheinfo can be built correctly, we need to initialize level
> > and type. Since RSIC-V currently does not have a register group that
> > describes cache-related attributes like ARM64, we cannot obtain them
> > directly, so now we obtain cache leaves from the ACPI PPTT table
> > (acpi_get_cache_info()) and set the cache type through split_levels.
> >
> > Suggested-by: Jeremy Linton <jeremy.linton at arm.com>
> > Suggested-by: Sudeep Holla <sudeep.holla at arm.com>
> > Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
> > ---
> >   arch/riscv/kernel/cacheinfo.c | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/arch/riscv/kernel/cacheinfo.c b/arch/riscv/kernel/cacheinfo.c
> > index 30a6878287ad..dc5fb70362f1 100644
> > --- a/arch/riscv/kernel/cacheinfo.c
> > +++ b/arch/riscv/kernel/cacheinfo.c
> > @@ -6,6 +6,7 @@
> >   #include <linux/cpu.h>
> >   #include <linux/of.h>
> >   #include <asm/cacheinfo.h>
> > +#include <linux/acpi.h>
> >
> >   static struct riscv_cacheinfo_ops *rv_cache_ops;
> >
> > @@ -78,6 +79,25 @@ int populate_cache_leaves(unsigned int cpu)
> >       struct device_node *prev = NULL;
> >       int levels = 1, level = 1;
> >
> > +     if (!acpi_disabled) {
> > +             int ret, idx, fw_levels, split_levels;
> > +
> > +             ret = acpi_get_cache_info(cpu, &fw_levels, &split_levels);
> > +             if (ret)
> > +                     return ret;
> > +
> > +             for (idx = 0; level <= this_cpu_ci->num_levels &&
> > +                  idx < this_cpu_ci->num_leaves; idx++, level++) {
>
> AFAIK the purpose of idx here it to assure that the number of cache
> leaves is not overflowing. But right below we are utilizing two of them
> at once, so this check isn't correct. OTOH, since its allocated as
> levels + split_levels I don't think its actually possible for this to
> cause a problem. Might be worthwhile to just hoist it before the loop
> and revalidate the total leaves about to be utilized.
>

Do you mean to modify the logic as follows to make it more complete?
for (idx = 0; level <= this_cpu_ci->num_levels &&
      idx < this_cpu_ci->num_leaves; level++) {
        if (level <= split_levels) {
               ci_leaf_init(this_leaf++, CACHE_TYPE_DATA, level);
               idx++;
               ci_leaf_init(this_leaf++, CACHE_TYPE_INST, level);
               idx++;
       } else {
               ci_leaf_init(this_leaf++, CACHE_TYPE_UNIFIED, level);
               idx++;
      }
}


Thanks,
Yunhui