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From: Anup Patel <anup@brainfault.org>
Date: Wed, 15 May 2024 19:15:56 +0530
Message-ID: <CAAhSdy12-_Hdb-WVrs8kyfCy_OQA0p27DS6TOV87dh9HODrU_Q@mail.gmail.com>
Subject: Re: [PATCH] cpuidle: riscv-sbi: Add cluster_pm_enter()/exit()
To: Nick Hu <nick.hu@sifive.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>, palmer@dabbelt.com, rafael@kernel.org, 
	daniel.lezcano@linaro.org, paul.walmsley@sifive.com, linux-pm@vger.kernel.org, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, 
	zong.li@sifive.com, Cyan Yang <cyan.yang@sifive.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Nick,

On Wed, May 15, 2024 at 5:45=E2=80=AFPM Nick Hu <nick.hu@sifive.com> wrote:
>
> Hi Anup,
>
> Thank you for your guidance.
> After enabling the debug message, we found a way to solve the problem
> by the following steps:
> 1. Add a compatible string in 'power-domains' node otherwise it won't
> be the supplier of the consumers. (See of_link_to_phandle())

Hmm, requiring a compatible string is odd. Where should we document
this compatible string ?

> 2. Move the 'power-domains' node outside the 'cpus' node otherwise it
> won't be added to the device hierarchy by device_add().
> 3. Update the cpuidle-riscv-sbi driver to get the pds_node from
> '/power-domains'.

By adding a compatible string and moving the "power-domains" node
outside, you are simply forcing the OF framework to populate devices.

How about manually creating platform_device for each power-domain
DT node using of_platform_device_create() in sbi_pd_init() ?

>
> So the DTS will be like:
> cpus {
>     ...
>      domain-idle-states {
>            CLUSTER_SLEEP:cluster-sleep {
>                         compatible =3D "domain-idle-state";
>                         ...
>             }
>      }
> }
> power-domains {
>             compatible =3D "riscv,sbi-power-domains"
>             ...
>             ...
>             CLUSTER_PD: clusterpd {
>                     domain-idle-states =3D <&CLUSTER_SLEEP>;
>             };
> }
> soc {
>       deviceA@xxx{
>              ...
>              power-domains =3D <&CLUSTER_PD>;
>              ...
>       }
> }

Regards,
Anup

>
> Regards,
> Nick
>
> On Tue, May 14, 2024 at 10:54=E2=80=AFPM Anup Patel <anup@brainfault.org>=
 wrote:
> >
> > On Tue, May 14, 2024 at 7:53=E2=80=AFPM Anup Patel <anup@brainfault.org=
> wrote:
> > >
> > > Hi Nick,
> > >
> > > On Tue, May 14, 2024 at 3:20=E2=80=AFPM Nick Hu <nick.hu@sifive.com> =
wrote:
> > > >
> > > > Hi Ulf,
> > > >
> > > > Thank you for your valuable suggestion.
> > > > I sincerely apologize for the delay in responding to your message. =
We
> > > > have diligently worked on experimenting with the suggestion you
> > > > provided.
> > > >
> > > > As per your recommendation, we have incorporated the "power-domains=
=3D<>
> > > > property" into the consumer's node, resulting in modifications to t=
he
> > > > DTS as illustrated below:
> > > >
> > > > cpus {
> > > >     ...
> > > >      domain-idle-states {
> > > >            CLUSTER_SLEEP:cluster-sleep {
> > > >                         compatible =3D "domain-idle-state";
> > > >                         ...
> > > >             }
> > > >      }
> > > >      power-domains {
> > > >             ...
> > > >             ...
> > > >             CLUSTER_PD: clusterpd {
> > > >                     domain-idle-states =3D <&CLUSTER_SLEEP>;
> > > >             };
> > > >      }
> > > > }
> > > > soc {
> > > >       deviceA@xxx{
> > > >              ...
> > > >              power-domains =3D <&CLUSTER_PD>;
> > > >              ...
> > > >       }
> > > > }
> > > >
> > > > However, this adjustment has led to an issue where the probe for
> > > > 'deviceA' is deferred by 'device_links_check_suppliers()' within
> > > > 'really_probe()'. In an attempt to mitigate this issue, we
> > > > experimented with a workaround by adding the attribute
> > > > "status=3D"disabled"" to the 'CLUSTER_PD' node. This action aimed t=
o
> > > > prevent the creation of a device link between 'deviceA' and
> > > > 'CLUSTER_PD'. Nevertheless, we remain uncertain about the
> > > > appropriateness of this solution.
> > > >
> > > > Do you have suggestions on how to effectively address this issue?
> > >
> > > I totally missed this email since I was not CC'ed sorry about that. P=
lease
> > > use get_maintainers.pl when sending patches.
> >
> > I stand corrected. This patch had landed in the "spam" folder. I don't =
know why.
> >
> > Regards,
> > Anup
> >
> > >
> > > The genpd_add_provider() (called by of_genpd_add_provider_simple())
> > > does mark the power-domain DT node as initialized (fwnode_dev_initial=
ized())
> > > so after the cpuidle-riscv-sbi driver is probed the 'deviceA' depende=
ncy is
> > > resolved and 'deviceA' should be probed unless there are other unmet
> > > dependencies.
> > >
> > > Try adding "#define DEBUG" before all includes in drivers/core/base.c
> > > and add "loglevel=3D8" in kernel parameters, this will print producer=
-consumer
> > > linkage of all devices.
> > >
> > > Marking the power-domain DT node as "disabled" is certainly not the
> > > right way.
> > >
> > > Regards,
> > > Anup
> > >
> > > >
> > > > Regards,
> > > > Nick
> > > >
> > > > On Tue, Apr 30, 2024 at 4:13=E2=80=AFPM Ulf Hansson <ulf.hansson@li=
naro.org> wrote:
> > > > >
> > > > > On Mon, 29 Apr 2024 at 18:26, Nick Hu <nick.hu@sifive.com> wrote:
> > > > > >
> > > > > > On Tue, Apr 30, 2024 at 12:22=E2=80=AFAM Nick Hu <nick.hu@sifiv=
e.com> wrote:
> > > > > > >
> > > > > > > Hi Ulf
> > > > > > >
> > > > > > > On Mon, Apr 29, 2024 at 10:32=E2=80=AFPM Ulf Hansson <ulf.han=
sson@linaro.org> wrote:
> > > > > > > >
> > > > > > > > On Mon, 26 Feb 2024 at 07:51, Nick Hu <nick.hu@sifive.com> =
wrote:
> > > > > > > > >
> > > > > > > > > When the cpus in the same cluster are all in the idle sta=
te, the kernel
> > > > > > > > > might put the cluster into a deeper low power state. Call=
 the
> > > > > > > > > cluster_pm_enter() before entering the low power state an=
d call the
> > > > > > > > > cluster_pm_exit() after the cluster woken up.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Nick Hu <nick.hu@sifive.com>
> > > > > > > >
> > > > > > > > I was not cced this patch, but noticed that this patch got =
queued up
> > > > > > > > recently. Sorry for not noticing earlier.
> > > > > > > >
> > > > > > > > If not too late, can you please drop/revert it? We should r=
eally move
> > > > > > > > away from the CPU cluster notifiers. See more information b=
elow.
> > > > > > > >
> > > > > > > > > ---
> > > > > > > > >  drivers/cpuidle/cpuidle-riscv-sbi.c | 24 +++++++++++++++=
+++++++--
> > > > > > > > >  1 file changed, 22 insertions(+), 2 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/cpuidle/cpuidle-riscv-sbi.c b/driver=
s/cpuidle/cpuidle-riscv-sbi.c
> > > > > > > > > index e8094fc92491..298dc76a00cf 100644
> > > > > > > > > --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> > > > > > > > > +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> > > > > > > > > @@ -394,6 +394,7 @@ static int sbi_cpuidle_pd_power_off(s=
truct generic_pm_domain *pd)
> > > > > > > > >  {
> > > > > > > > >         struct genpd_power_state *state =3D &pd->states[p=
d->state_idx];
> > > > > > > > >         u32 *pd_state;
> > > > > > > > > +       int ret;
> > > > > > > > >
> > > > > > > > >         if (!state->data)
> > > > > > > > >                 return 0;
> > > > > > > > > @@ -401,6 +402,10 @@ static int sbi_cpuidle_pd_power_off(=
struct generic_pm_domain *pd)
> > > > > > > > >         if (!sbi_cpuidle_pd_allow_domain_state)
> > > > > > > > >                 return -EBUSY;
> > > > > > > > >
> > > > > > > > > +       ret =3D cpu_cluster_pm_enter();
> > > > > > > > > +       if (ret)
> > > > > > > > > +               return ret;
> > > > > > > >
> > > > > > > > Rather than using the CPU cluster notifiers, consumers of t=
he genpd
> > > > > > > > can register themselves to receive genpd on/off notifiers.
> > > > > > > >
> > > > > > > > In other words, none of this should be needed, right?
> > > > > > > >
> > > > > > > Thanks for the feedback!
> > > > > > > Maybe I miss something, I'm wondering about a case like below=
:
> > > > > > > If we have a shared L2 cache controller inside the cpu cluste=
r power
> > > > > > > domain and we add this controller to be a consumer of the pow=
er
> > > > > > > domain, Shouldn't the genpd invoke the domain idle only after=
 the
> > > > > > > shared L2 cache controller is suspended?
> > > > > > > Is there a way that we can put the L2 cache down while all cp=
us in the
> > > > > > > same cluster are idle?
> > > > > > > > [...]
> > > > > > Sorry, I made some mistake in my second question.
> > > > > > Update the question here:
> > > > > > Is there a way that we can save the L2 cache states while all c=
pus in the
> > > > > > same cluster are idle and the cluster could be powered down?
> > > > >
> > > > > If the L2 cache is a consumer of the cluster, the consumer driver=
 for
> > > > > the L2 cache should register for genpd on/off notifiers.
> > > > >
> > > > > The device representing the L2 cache needs to be enabled for runt=
ime
> > > > > PM, to be taken into account correctly by the cluster genpd. In t=
his
> > > > > case, the device should most likely remain runtime suspended, but
> > > > > instead rely on the genpd on/off notifiers to understand when
> > > > > save/restore of the cache states should be done.
> > > > >
> > > > > Kind regards
> > > > > Uffe