Re: [PATCH v4] kernel.h: add comments for system_states

Mauro Carvalho Chehab
2025-09-05T13:38:47Z

On Fri, Sep 05, 2025 at 04:06:31PM +0300, Jani Nikula wrote:
> On Fri, 05 Sep 2025, Mauro Carvalho Chehab <mchehab+huawei@kernel.org> wrote:
> > Em Fri, 05 Sep 2025 12:02:37 +0300
> > Jani Nikula <jani.nikula@linux.intel.com> escreveu:
> >
> >> On Wed, 03 Sep 2025, Randy Dunlap <rdunlap@infradead.org> wrote:
> >> > Provide some basic comments about the system_states and what they imply.
> >> > Also convert the comments to kernel-doc format.
> >> >
> >> > However, kernel-doc does not support kernel-doc notation on extern
> >> > struct/union/typedef/enum/etc. So I made this a DOC: block so that
> >> > I can use (insert) it into a Documentation (.rst) file and have it
> >> > look decent.
> >>
> >> The simple workaround is to separate the enum type and the variable:
> >>
> >> /**
> >> * kernel-doc for the enum
> >> */
> >> enum system_states {
> >> ...
> >> };
> >>
> >> /**
> >> * kernel-doc for the variable
> >> */
> >> extern enum system_states system_state;
> >>
> >> BR,
> >> Jani.
> >>
> >> >
> >> > Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> >> > Acked-by: Rafael J. Wysocki <rafael@kernel.org> # v1
> >> > ---
> >> > v2: add Rafael's Ack.
> >> > v3: add Andrew
> >> > v4: add DOC: so that this DOC: block can be used in Documentation/
> >> > add Greg K-H
> >> > add Jon Corbet, Mauro Chehab, & linux-doc
> >> >
> >> > Cc: Andrew Morton <akpm@linux-foundation.org>
> >> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> >> > Cc: Pavel Machek <pavel@ucw.cz>
> >> > Cc: Len Brown <len.brown@intel.com>
> >> > Cc: linux-pm@vger.kernel.org
> >> > Cc: Jonathan Corbet <corbet@lwn.net>
> >> > Cc: linux-doc@vger.kernel.org
> >> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> >> > Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
> >> > ---
> >> > Documentation/driver-api/pm/devices.rst | 8 ++++++++
> >> > include/linux/kernel.h | 18 ++++++++++++++++--
> >> > 2 files changed, 24 insertions(+), 2 deletions(-)
> >> >
> >> > --- linux-next-20250819.orig/include/linux/kernel.h
> >> > +++ linux-next-20250819/include/linux/kernel.h
> >> > @@ -164,8 +164,22 @@ extern int root_mountflags;
> >> >
> >> > extern bool early_boot_irqs_disabled;
> >> >
> >> > -/*
> >> > - * Values used for system_state. Ordering of the states must not be changed
> >> > +/**
> >> > + * DOC: General system_states available for drivers
> >> > + *
> >> > + * enum system_states - Values used for system_state.
> >> > + *
> >> > + * * @SYSTEM_BOOTING: %0, no init needed
> >> > + * * @SYSTEM_SCHEDULING: system is ready for scheduling; OK to use RCU
> >> > + * * @SYSTEM_FREEING_INITMEM: system is freeing all of initmem; almost running
> >> > + * * @SYSTEM_RUNNING: system is up and running
> >> > + * * @SYSTEM_HALT: system entered clean system halt state
> >> > + * * @SYSTEM_POWER_OFF: system entered shutdown/clean power off state
> >> > + * * @SYSTEM_RESTART: system entered emergency power off or normal restart
> >> > + * * @SYSTEM_SUSPEND: system entered suspend or hibernate state
> >> > + *
> >> > + * Note:
> >> > + * Ordering of the states must not be changed
> >> > * as code checks for <, <=, >, >= STATE.
> >> > */
> >> > extern enum system_states {
> >> > --- linux-next-20250819.orig/Documentation/driver-api/pm/devices.rst
> >> > +++ linux-next-20250819/Documentation/driver-api/pm/devices.rst
> >> > @@ -241,6 +241,14 @@ before reactivating its class I/O queues
> >> > More power-aware drivers might prepare the devices for triggering system wakeup
> >> > events.
> >> >
> >> > +System states available for drivers
> >> > +-----------------------------------
> >> > +
> >> > +These system states are available for drivers to help them determine how to
> >> > +handle state transitions.
> >> > +
> >> > +.. kernel-doc:: include/linux/kernel.h
> >> > + :doc: General system_states available for drivers
> >> >
> >> > Call Sequence Guarantees
> >> > ------------------------
> >> >
> >>
> >
> > If the problem is with "extern" before enum, fixing kdoc be
> > fairly trivial.
>
> The non-trivial part is deciding whether you're documenting the enum
> type or the variable. Both are equally valid options.

True.

I'd say that, if the variable is under EXPORT_SYMBOL macros, it
should be documented.

The same applies to the enum: if it is used by kAPI, it should
also be documented.

So, yeah, I suspect that on most kAPI cases, the best is to split,
having documentation for both.

>
> BR,
> Jani.
>
> >
> > If you see:
> >
> > def dump_function(self, ln, prototype):
> >
> > # Prefixes that would be removed
> > sub_prefixes = [
> > ...
> > (r"^extern +", "", 0),
> > ...
> > }
> >
> > for search, sub, flags in sub_prefixes:
> > prototype = KernRe(search, flags).sub(sub, prototype)
> >
> >
> > we need something similar to that at:
> > def dump_enum(self, ln, proto):
> >
> > alternatively, we could use a simpler approach modifying adding a
> > non-group optional match for "extern". E.g:
> >
> > - r = KernRe(r'enum\s+(\w*)\s*\{(.*)\}')
> > + r = KernRe(r'(?:extern\s+)?enum\s+(\w*)\s*\{(.*)\}')
> >
> > (untested)
> >
> > Regards,
> > Mauro
> >
> >
> > Thanks,
> > Mauro
>
> --
> Jani Nikula, Intel

--
Thanks,
Mauro