Re: [PATCHv1] ACPI: processor idle: Allow playing dead in C3 state

[Lazar, Lijo]

On 9/28/2021 7:18 PM, Rafael J. Wysocki wrote:
> On Tue, Sep 28, 2021 at 3:00 PM Gong, Richard <richard.gong@xxxxxxx> wrote:
> > Hi Rafael,
> >
> > On 9/24/2021 11:31 AM, Rafael J. Wysocki wrote:
> > > On Wed, Sep 22, 2021 at 3:31 PM Richard Gong <richard.gong@xxxxxxx> wrote:
> > > > When some cores are disabled on AMD platforms, the system will no longer
> > > > be able to enter suspend-to-idle s0ix.
> > > >
> > > > Update to allow playing dead in C3 state so that the CPUs can enter the
> > > > deepest state on AMD platforms.
> > > >
> > > > BugLink: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Famd%2F-%2Fissues%2F1708&amp;data=04%7C01%7Clijo.lazar%40amd.com%7C44c85e9ae1dd4bec087e08d98286aa72%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637684337168161919%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=Qoh%2BwD%2B1JzPYBc0rrGfNCdQWY1pKo8WBhLPmsmQ6G%2Bo%3D&amp;reserved=0
> > > > Suggested-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > > Signed-off-by: Richard Gong <richard.gong@xxxxxxx>
> > > > ---
> > > >    drivers/acpi/processor_idle.c | 3 ++-
> > > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > > > index f37fba9e5ba0..61d5a72d218e 100644
> > > > --- a/drivers/acpi/processor_idle.c
> > > > +++ b/drivers/acpi/processor_idle.c
> > > > @@ -789,7 +789,8 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
> > > >                   state->enter = acpi_idle_enter;
> > > >
> > > >                   state->flags = 0;
> > > > -               if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2) {
> > > > +               if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2
> > > > +                       || cx->type == ACPI_STATE_C3) {
> > > >                           state->enter_dead = acpi_idle_play_dead;
> > > >                           drv->safe_state_index = count;
> > > >                   }
> > > > --
> > > Tentatively applied as 5.16 material, but have you done any research
> > > on why this restriction has been there in the first place?
> >
> > Yes, we need this change to align with the updated firmware on AMD
> > platforms.
>
> Well, it wouldn't be necessary to change the code otherwise.
>
> Still, without the patch it is not allowed to play dead in deep idle
> states (C3 type) and do you know why?

Found the original patch thread, unfortunately there is no discussion on 
why C3 was skipped or not allowed - 
https://www.spinics.net/lists/linux-pm/msg27003.html

Maybe, Intel CPU offlining worked through MWAITs and AMD bothered only 
till C2.

Thanks,
Lijo

> Or IOW how likely is this change to break anything on legacy platforms?