Re: [PATCH v5 1/2] PM / Domains: Add support for 'required-opps' to set default perf state

[Ulf Hansson]

On Wed, 4 Aug 2021 at 13:08, Rajendra Nayak <rnayak@xxxxxxxxxxxxxx> wrote:
>
>
> On 8/3/2021 10:08 AM, Rajendra Nayak wrote:
> >
> > On 8/2/2021 6:29 PM, Ulf Hansson wrote:
> >> On Tue, 20 Jul 2021 at 09:12, Rajendra Nayak <rnayak@xxxxxxxxxxxxxx> wrote:
> >>>
> >>> Some devices within power domains with performance states do not
> >>> support DVFS, but still need to vote on a default/static state
> >>> while they are active. They can express this using the 'required-opps'
> >>> property in device tree, which points to the phandle of the OPP
> >>> supported by the corresponding power-domains.
> >>>
> >>> Add support to parse this information from DT and then set the
> >>> specified performance state during attach and drop it on detach.
> >>> runtime suspend/resume callbacks already have logic to drop/set
> >>> the vote as needed and should take care of dropping the default
> >>> perf state vote on runtime suspend and restore it back on runtime
> >>> resume.
> >>>
> >>> Signed-off-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> >>> ---
> >>>   drivers/base/power/domain.c | 28 +++++++++++++++++++++++++---
> >>>   include/linux/pm_domain.h   |  1 +
> >>>   2 files changed, 26 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> >>> index a934c67..f454031 100644
> >>> --- a/drivers/base/power/domain.c
> >>> +++ b/drivers/base/power/domain.c
> >>> @@ -2598,6 +2598,12 @@ static void genpd_dev_pm_detach(struct device *dev, bool power_off)
> >>>
> >>>          dev_dbg(dev, "removing from PM domain %s\n", pd->name);
> >>>
> >>> +       /* Drop the default performance state */
> >>> +       if (dev_gpd_data(dev)->default_pstate) {
> >>> +               dev_pm_genpd_set_performance_state(dev, 0);
> >>> +               dev_gpd_data(dev)->default_pstate = 0;
> >>> +       }
> >>> +
> >>>          for (i = 1; i < GENPD_RETRY_MAX_MS; i <<= 1) {
> >>>                  ret = genpd_remove_device(pd, dev);
> >>>                  if (ret != -EAGAIN)
> >>> @@ -2635,9 +2641,10 @@ static void genpd_dev_pm_sync(struct device *dev)
> >>>   static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
> >>>                                   unsigned int index, bool power_on)
> >>>   {
> >>> +       struct device_node *np;
> >>>          struct of_phandle_args pd_args;
> >>>          struct generic_pm_domain *pd;
> >>> -       int ret;
> >>> +       int ret, pstate;
> >>>
> >>>          ret = of_parse_phandle_with_args(dev->of_node, "power-domains",
> >>>                                  "#power-domain-cells", index, &pd_args);
> >>> @@ -2675,10 +2682,25 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
> >>>                  genpd_unlock(pd);
> >>>          }
> >>>
> >>> -       if (ret)
> >>> +       if (ret) {
> >>>                  genpd_remove_device(pd, dev);
> >>> +               return -EPROBE_DEFER;
> >>> +       }
> >>> +
> >>> +       /* Set the default performance state */
> >>> +       np = base_dev->of_node;
> >>
> >> Please use dev->of_node instead (it is set to the same of_node as
> >> base_dev by the callers of __genpd_dev_pm_attach) as it's more
> >> consistent with existing code.
> >>
> >>> +       if (of_parse_phandle(np, "required-opps", index)) {
> >>> +               pstate = of_get_required_opp_performance_state(np, index);
> >>> +               if (pstate < 0) {
> >>> +                       ret = pstate;
> >>> +                       dev_err(dev, "failed to set required performance state for power-domain %s: %d\n",
> >>> +                               pd->name, ret);
> >>> +               }
> >>> +               dev_pm_genpd_set_performance_state(dev, pstate);
> >>> +               dev_gpd_data(dev)->default_pstate = pstate;
> >>
> >> This doesn't look entirely correct to me. If we fail to translate a
> >> required opp to a performance state, we shouldn't try to set it.
> >
> > yeah, that does not seem right at all :(
> >
> >> Perhaps it's also easier to call
> >> of_get_required_opp_performance_state() unconditionally of whether a
> >> "required-opps" specifier exists. If it fails with the translation,
> >> then we just skip setting a default state and continue with returning
> >> 1.
> >>
> >> Would that work?
>
> Looks like calling of_get_required_opp_performance_state() unconditionally
> makes it spit out a pr_err() in case the node is missing "required-opps" property,
> so I posted a v6 [1] with the check in place and adding the missing else
> condition.

I see.

Viresh, would it make sense to remove that print? I mean, the
required-opps property could be considered as optional and it seems a
bit silly that a pre-parsing of the property is needed to figure that
out.

>
> [1] https://lore.kernel.org/patchwork/project/lkml/list/?series=510727

Kind regards
Uffe