On Tue, Oct 8, 2024 at 8:24 PM Rafael J. Wysocki [off-list ref] wrote:

On Tue, Oct 8, 2024 at 12:35 AM Ulf Hansson [off-list ref] wrote:

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On Tue, 8 Oct 2024 at 00:25, Laurent Pinchart
[off-list ref] wrote:

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Hi Ulf,

On Tue, Oct 08, 2024 at 12:08:24AM +0200, Ulf Hansson wrote:

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On Mon, 7 Oct 2024 at 20:49, Laurent Pinchart wrote:

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On Fri, Oct 04, 2024 at 04:38:36PM +0200, Ulf Hansson wrote:

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On Fri, 4 Oct 2024 at 11:41, Sakari Ailus wrote:

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Hello everyone,

This set will switch the users of pm_runtime_put_autosuspend() to
__pm_runtime_put_autosuspend() while the former will soon be re-purposed
to include a call to pm_runtime_mark_last_busy(). The two are almost
always used together, apart from bugs which are likely common. Going
forward, most new users should be using pm_runtime_put_autosuspend().

Once this conversion is done and pm_runtime_put_autosuspend() re-purposed,
I'll post another set to merge the calls to __pm_runtime_put_autosuspend()
and pm_runtime_mark_last_busy().

That sounds like it could cause a lot of churns.

Why not add a new helper function that does the
pm_runtime_put_autosuspend() and the pm_runtime_mark_last_busy()
things? Then we can start moving users over to this new interface,
rather than having this intermediate step?

I think the API would be nicer if we used the shortest and simplest
function names for the most common use cases. Following
pm_runtime_put_autosuspend() with pm_runtime_mark_last_busy() is that
most common use case. That's why I like Sakari's approach of repurposing
pm_runtime_put_autosuspend(), and introducing
__pm_runtime_put_autosuspend() for the odd cases where
pm_runtime_mark_last_busy() shouldn't be called.

Okay, so the reason for this approach is because we couldn't find a
short and descriptive name that could be used in favor of
pm_runtime_put_autosuspend(). Let me throw some ideas at it and maybe
you like it - or not. :-)

I like the idea at least :-)

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I don't know what options you guys discussed, but to me the entire
"autosuspend"-suffix isn't really that necessary in my opinion. There
are more ways than calling pm_runtime_put_autosuspend() that triggers
us to use the RPM_AUTO flag for rpm_suspend(). For example, just
calling pm_runtime_put() has the similar effect.

To be honest, I'm lost there. pm_runtime_put() calls
__pm_runtime_idle(RPM_GET_PUT | RPM_ASYNC), while
pm_runtime_put_autosuspend() calls __pm_runtime_suspend(RPM_GET_PUT |
RPM_ASYNC | RPM_AUTO).

__pm_runtime_idle() ends up calling rpm_idle(), which may call
rpm_suspend() - if it succeeds to idle the device. In that case, it
tags on the RPM_AUTO flag in the call to rpm_suspend(). Quite similar
to what is happening when calling pm_runtime_put_autosuspend().

Right.

For almost everybody, except for a small bunch of drivers that
actually have a .runtime_idle() callback, pm_runtime_put() is
literally equivalent to pm_runtime_put_autosuspend().

So really the question is why anyone who doesn't provide a
.runtime_idle() callback bothers with using this special
pm_runtime_put_autosuspend() thing, which really means "do a
runtime_put(), but skip my .runtime_idle() callback".

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Moreover, it's similar for pm_runtime_mark_last_busy(), it's called
during rpm_resume() too, for example. So why bother about having
"mark_last_busy" in the new name too.

That said, my suggestion is simply "pm_runtime_put_suspend".

Can we do even better, and make pm_runtime_put() to handle autosuspend
automatically when autosuspend is enabled ?

As stated above, this is already the case.

What really is needed appears to be a combination of
pm_runtime_mark_last_busy() with pm_runtime_put().

Granted, pm_runtime_put() could do the pm_runtime_mark_last_busy()
thing automatically if autosuspend is enabled and the only consequence
of it might be delaying a suspend of the device until its autosuspend
timer expires, which should not be a problem in the vast majority of
cases.

That said, it is likely better to avoid surprising the current users
of pm_runtime_put() and define something like

static inline void pm_runtime_touch_and_put(struct device *dev)
{
        pm_runtime_mark_last_busy(dev);
        pm_runtime_put(dev);
}