Re: [PATCH 1/2] OPP: Use _set_opp_level() for single genpd case

Stephan Gerhold
2023-10-25T13:49:21Z

On Wed, Oct 25, 2023 at 12:40:26PM +0200, Ulf Hansson wrote:
> On Wed, 25 Oct 2023 at 08:55, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> >
> > On 19-10-23, 13:16, Ulf Hansson wrote:
> > > On Thu, 19 Oct 2023 at 12:22, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > > > +static int _link_required_opps(struct dev_pm_opp *opp, struct opp_table *opp_table,
> > > > struct opp_table *required_table, int index)
> > > > {
> > > > struct device_node *np;
> > > > @@ -314,6 +314,25 @@ static int _link_required_opps(struct dev_pm_opp *opp,
> > > > return -ENODEV;
> > > > }
> > > >
> > > > + /*
> > > > + * There are two genpd (as required-opp) cases that we need to handle,
> > > > + * devices with a single genpd and ones with multiple genpds.
> > > > + *
> > > > + * The single genpd case requires special handling as we need to use the
> > > > + * same `dev` structure (instead of a virtual one provided by genpd
> > > > + * core) for setting the performance state. Lets treat this as a case
> > > > + * where the OPP's level is directly available without required genpd
> > > > + * link in the DT.
> > > > + *
> > > > + * Just update the `level` with the right value, which
> > > > + * dev_pm_opp_set_opp() will take care of in the normal path itself.
> > > > + */
> > > > + if (required_table->is_genpd && opp_table->required_opp_count == 1 &&
> > > > + !opp_table->genpd_virt_devs) {
> > > > + if (!WARN_ON(opp->level))
> > >
> > > Hmm. Doesn't this introduce an unnecessary limitation?
> > >
> > > An opp node that has a required-opps phande, may have "opp-hz",
> > > "opp-microvolt", etc. Why would we not allow the "opp-level" to be
> > > used too?
> >
> > Coming back to this, why would we ever want a device to have "opp-level" and
> > "required-opp" (set to genpd's table) ? That would mean we will call:
> >
> > dev_pm_domain_set_performance_state() twice to set different level values.
>
> Yes - and that would be weird, especially since the PM domain (genpd)
> is already managing the aggregation and propagation to parent domains.
>

FWIW I'm hitting this WARNing when trying to set up the parent domain
setup for CPR->RPMPD(MX) on MSM8916 that I discussed with Uffe recently
[1]. I know, me and all my weird OPP setups. :'D

Basically, I have cpufreq voting for performance states of the CPR genpd
(via required-opps). CPR is supposed to have <&rpmpd MSM8916_VDDMX_AO>
as parent genpd and translates to the parent performance state using the
"required-opps" in the *CPR* OPP table:

cpr: power-controller@b018000 {
compatible = "qcom,msm8916-cpr", "qcom,cpr";
reg = <0x0b018000 0x1000>;
/* ... */
#power-domain-cells = <0>;
operating-points-v2 = <&cpr_opp_table>;
/* Supposed to be parent domain, not consumer */
power-domains = <&rpmpd MSM8916_VDDMX_AO>;

cpr_opp_table: opp-table {
compatible = "operating-points-v2-qcom-level";

cpr_opp1: opp1 {
opp-level = <1>;
qcom,opp-fuse-level = <1>;
required-opps = <&rpmpd_opp_svs_soc>;
};
cpr_opp2: opp2 {
opp-level = <2>;
qcom,opp-fuse-level = <2>;
required-opps = <&rpmpd_opp_nom>;
};
cpr_opp3: opp3 {
opp-level = <3>;
qcom,opp-fuse-level = <3>;
required-opps = <&rpmpd_opp_super_turbo>;
};
};
};

There are two problems with this:

1. (Unrelated to $subject patch)
Since there is only a single entry in "power-domains", the genpd
core code automatically attaches the CPR platform device as consumer
of the VDDMX_AO power domain. I don't want this, I want it to become
child of the VDDMX_AO genpd.

I added some hacky code to workaround this. One option that works is
to add a second dummy entry to "power-domains", which will prevent
the genpd core from attaching the power domain:

power-domains = <&rpmpd MSM8916_VDDMX_AO>, <0>;

The other option is detaching the power domain again in probe(),
after setting it up as parent domain:

struct of_phandle_args parent, child;

child.np = dev->of_node;
child.args_count = 0;

of_parse_phandle_with_args(dev->of_node, "power-domains",
"#power-domain-cells", 0, &parent));
of_genpd_add_subdomain(&parent, &child);

/* Detach power domain since it's managed via the subdomain */
dev_pm_domain_detach(dev, false);

Is there a cleaner way to handle this? Mainly a question for Uffe.

2. The OPP WARNing triggers with both variants because it just checks
if "required-opps" has a single entry. I guess we need extra checks
to exclude the "parent genpd" case compared to the "OPP" case.

[ 1.116244] WARNING: CPU: 2 PID: 36 at drivers/opp/of.c:331 _link_required_opps+0x180/0x1cc
[ 1.125897] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
[ 1.146887] pc : _link_required_opps+0x180/0x1cc
[ 1.146902] lr : _link_required_opps+0xdc/0x1cc
[ 1.276408] Call trace:
[ 1.283519] _link_required_opps+0x180/0x1cc
[ 1.285779] _of_add_table_indexed+0x61c/0xd40
[ 1.290292] dev_pm_opp_of_add_table+0x10/0x18
[ 1.294546] of_genpd_add_provider_simple+0x80/0x160
[ 1.298974] cpr_probe+0x6a0/0x97c
[ 1.304092] platform_probe+0x64/0xbc

It does seem to work correctly, with and without this patch. So I guess
another option might be to simply silence this WARN_ON(). :')

Thanks,
Stephan

[1]: https://lore.kernel.org/linux-pm/CAPDyKFoH5EOvRRKy-Bgp_B9B3rf=PUKK5N45s5PNgfBi55PaOQ@mail.gmail.com/