Message-ID: <41a0ad69-912b-4eb3-84f7-fb385433c056@opensource.cirrus.com>
Date: Wed, 9 Oct 2024 13:48:15 +0100
From: Richard Fitzgerald <rf@...nsource.cirrus.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson
	<ulf.hansson@...aro.org>,
        Laurent Pinchart
	<laurent.pinchart@...asonboard.com>,
        Sakari Ailus
	<sakari.ailus@...ux.intel.com>
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Subject: Re: [PATCH 00/51] treewide: Switch to __pm_runtime_put_autosuspend()

On 08/10/2024 7:24 pm, Rafael J. Wysocki wrote:
> On Tue, Oct 8, 2024 at 12:35 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>
>> 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().
> 
> 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,

Because they are following the documentation? It says:

"Drivers should call pm_runtime_mark_last_busy() to update this field
after carrying out I/O, typically just before calling
pm_runtime_put_autosuspend()."

and

"In order to use autosuspend, subsystems or drivers must call
pm_runtime_use_autosuspend() (...), and thereafter they should use the
various `*_autosuspend()` helper functions instead of the non#
autosuspend counterparts"

So the documentation says I should be using pm_runtime_put_autosuspend()
instead of pm_runtime_put().

Seems unfair to criticise people for following the documentation.

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