Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive

[Tomeu Vizoso <tomeu.vizoso@collabora.com>]

On 19 May 2015 at 19:49, Alan Stern <stern@rowland.harvard.edu> wrote:
> On Tue, 19 May 2015, Tomeu Vizoso wrote:
>
>> This function makes less cumbersome to enable runtime PM in a device and
>> its descendants.
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
>
> I don't see the point of this.  In the scenario you have in mind, are
> the device and all its descendants registered by the same
> subsystem/driver?

Not quite, the scenario here is a driver (uvcvideo) that deals with a
specific piece of hardware and knows that all the descendants of the
device it's bound to are virtual.

The subtree is:

1-1:1.0 (bound to uvcvideo)
        ep_87
        input4
                event4
        media0
        video0

I liked how the force_direct_complete flag played out here, but I
agree with Rafael that it can be abused as the PM domain or the bus
type weren't able to prevent going directly to complete.

This is my testing branch, btw:

https://git.collabora.com/cgit/user/tomeu/linux.git/log/?h=fast-resume-v5

> If they are, can't the subsystem/driver code enable
> runtime PM for each of them when they are registered, by adding a
> single call in the right spot?
>
> If they don't all belong to the same subsystem/driver, who is going to
> call your pm_runtime_enable_recursive routine?  No single caller will
> have the right to enable runtime PM for all these devices.

Yeah, I was thinking that uvcvideo might be able to decide that, but
I'm not really sure about it.

Thanks,

Tomeu

> Alan Stern
>
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