Re: [PATCH 2/5] cpufreq: loongson3: Adjust the width of id and val in smc_message

Hi, Zhongqiu,

On Thu, Aug 20, 2026 at 6:03 PM Zhongqiu Han
<[email protected]> wrote:
>
> Hi Huacai,
>
> Please feel free to comment on the question below, or simply ignore it
> if you do not think it is worth addressing from an architectural
> perspective.
>
> On 8/18/2026 8:39 PM, Huacai Chen wrote:
> > The id field of smc_message is usually stand for the CPU ID. In the past
> > this driver was only tested for desktop and laptop productions so 4-bits
> > are enough. But now we have servers that can have as many as 256 cores,
> > so we need 8-bits CPU ID.
> >
> > On the other hand, the val field is usually stand for CPU frequency so
> > 12-bits are enough to represent 4GHz, and for higher frequencies there
> > is an extra bit to extend (enough for 8GHz).
>
> The extra bit appears to be unused in the current implementation.
> Perhaps it would be better to enforce the limit explicitly for id and
> val bits, for example by using FIELD_MAX().
OK, we can do it in the future.

>
> >
> > In theory, this is a incompatible change, but fortunately the old SMC
> > firmwares are not widely shipped and can be updated on the air, thus we
> > can safely adjust the widths.
>
> Not sure if using CMD_GET_VERSION check can avoid such incompatible
> issue?
Since the original SMC firmware and the current one has the same
version number and the current one was shipped widely, we can no
longer use CMD_GET_VERSION here.

Huacai

>
> >
> > Cc: [email protected]
> > Signed-off-by: Hongliang Wang <[email protected]>
> > Signed-off-by: Huacai Chen <[email protected]>
> > ---
> >   drivers/cpufreq/loongson3_cpufreq.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpufreq/loongson3_cpufreq.c b/drivers/cpufreq/loongson3_cpufreq.c
> > index 1e8715ea1b77..630f679aa739 100644
> > --- a/drivers/cpufreq/loongson3_cpufreq.c
> > +++ b/drivers/cpufreq/loongson3_cpufreq.c
> > @@ -21,9 +21,9 @@
> >   union smc_message {
> >       u32 value;
> >       struct {
> > -             u32 id          : 4;
> > +             u32 id          : 8;
> >               u32 info        : 4;
> > -             u32 val         : 16;
> > +             u32 val         : 12;
> >               u32 cmd         : 6;
> >               u32 extra       : 1;
> >               u32 complete    : 1;
>
>
> --
> Thx and BRs,
> Zhongqiu Han