Re: [RFC PATCH] PM / Runtime: Allow to inactivate devices during system suspend

[Ulf Hansson <ulf.hansson@linaro.org>]

On 15 November 2013 10:29, Bjørn Mork <bjorn@mork.no> wrote:
> Ulf Hansson <ulf.hansson@linaro.org> writes:
>
>> I think it is kind of strange to give provision to userspace to
>> control a "request based" power management feature in the kernel. Me
>> personally can't think of any good use case, but I comes from the
>> embedded/ARM world so I might not have the full picture.
>
> Because resuming a device inevitably adds latency, and that only
> userspace can decide the latency vs power policy for any given device,
> system and user?

That is a valid point. Though we have pm_qos, should not that be the
input for these kind of requirement for a driver?

In other words, if the latency requirement can't be met for a device
while re-activating it, it should not enter runtime suspend state.

>
> There are also other reasons, mostly related to device bugs.  But the
> above is the most important in my view.  Without that control knob I
> don't think I would have enabled runtime PM in any network driver while
> the netif is running.  The additional latency is noticable.
>
> Anyway, this is a pointless discussion.  The power/control ABI is in use
> so many places that it cannot be changed.  I'd suggest googling "break
> userspace" before even suggesting anything like that again.
>

I agree, and has never been a suggestion from my side either, more
like a statement that I don't like the sysfs for runtime PM. :-)

Kind regards
Ulf Hansson

>
> Bjørn