Re: [PATCH 0/3] PM / core: Invent a WAKEUP_POWERED driver flag

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: "Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Linux PM list <linux-pm@vger.kernel.org>,
	Kevin Hilman <khilman@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Simon Horman <horms@verge.net.au>,
	Niklas Soderlund <niklas.soderlund+renesas@ragnatech.se>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH 0/3] PM / core: Invent a WAKEUP_POWERED driver flag
Date: Thu, 9 Nov 2017 15:41:33 +0100	[thread overview]
Message-ID: <CAMuHMdUTX+=SfzivXz5HkgmrxcKB0miYnisBuy3iMtZNABS5KA@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFp6FYX-dLZJV6oto8Uc8e8KzO18ScTO8SU+8=NGbs7cOg@mail.gmail.com>

Hi Ulf,

On Thu, Nov 9, 2017 at 3:28 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> [...]
>
>>>> The Ethernet driver can still call device_set_wakeup_enable(... , false)
>>>> to control this.  If WoL is disabled by the user (or deemed not usable, see
>>>> below), it already does so.
>>>
>>> I don't think that API is intended to be used like that and I wonder
>>> if it even works as expected.
>>>
>>> Quoting the doc:
>>> "If device wakeup mechanisms are enabled or disabled directly by
>>> drivers, they also should use :c:func:`device_may_wakeup()` to decide what to do
>>> during a system sleep transition.  Device drivers, however, are not expected to
>>> call :c:func:`device_set_wakeup_enable()` directly in any case."
>>>
>>> Rafael, can you comment on this?
>>
>> There are ca. 100 callers in drivers.
>
> Yeah, but those doesn't normally use it to toggle the setting, but
> instead only to set a default value during ->probe() or whatever
> initialization code that runs.
>
> I think that makes a big difference, doesn't it?

The few Ethernet drivers I looked at change the state in their
ethtool_ops.set_wol() callback, not during probe.
This is to be configured from userspace using ethtool.

>>>> In addition, keeping WoL enabled for cases 1 and 2 may be desirable
>>>> (e.g allow wake-up if a cable is plugged in during system suspend and
>>>>  a magic packet is received afterwards), depending on the hardware.
>>>> But the driver can already control that through device_set_wakeup_enable().
>>>
>>> Ehh, that sounds weird. :-) If the Ethernet interface is down, how
>>> would such packet be received?
>>
>> It depends on your meaning of "up".  My interpretation is that "up" means
>> ready to handle packets between physical media and the Linux networking stack.
>>
>> So even when "down", the actual Ethernet controller may still be able to
>> receive a magic packet if WoL is enabled.  The magic packet is really a
>> magic packet not intended to be transmitted to the networking stack, but
>> merely serves as a wakeup signal.
>
> I see! So, in the end this seems like a combination of what the HW
> supports and what the user policy is set to.
>
> Out of curiosity, can you tell how those Renesas Ethernet devices
> works in this regards?

I don't know, I was just playing the devil's advocate ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds