linux-kernel - Re: [PATCH 00/51] treewide: Switch to __pm_runtime_put

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Message-ID: <CAPDyKFrGNwna6Y2pqSRaBbRYHKRaD2ayqQHLtoqLPOu9Et7qTg@mail.gmail.com>
Date: Tue, 8 Oct 2024 00:34:49 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, dri-devel@...ts.freedesktop.org, 
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	Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 00/51] treewide: Switch to __pm_runtime_put_autosuspend()

On Tue, 8 Oct 2024 at 00:25, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ulf,
>
> On Tue, Oct 08, 2024 at 12:08:24AM +0200, Ulf Hansson wrote:
> > On Mon, 7 Oct 2024 at 20:49, Laurent Pinchart wrote:
> > > On Fri, Oct 04, 2024 at 04:38:36PM +0200, Ulf Hansson wrote:
> > > > On Fri, 4 Oct 2024 at 11:41, Sakari Ailus wrote:
> > > > >
> > > > > 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 :-)
>
> > 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().

>
> >
> > 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.

>
> > If you don't like it, I will certainly not object to your current
> > approach, even if I think it leads to unnecessary churns.
> >
> > [...]
> >
> > Kind regards
> > Uffe
>
> --
> Regards,
>
> Laurent Pinchart

Kind regards
Uffe