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SubjectRe: [PATCH 0/8] Suspend block api (version 6)
Date
On Monday 10 May 2010, Kevin Hilman wrote:
> Hello,

Hi Kevin,

> I think many folks are still confused about exactly the problem being
> solved by this series as well as mixed up between opportunistic
> suspend and suspend blockers. Also, how this series impatcs the rest
> of the kernel (especially PM-aware drivers and subsystems) has caused
> a bit of confusion.
>
> To help with the confusion, I think a much clearer description of the
> problem being solved and the proposed solution is needed.
>
> To that end, I created a starting point for that below which
> summarizes how I understand the problem and the proposed solution, but
> of course this should be filled out in more detail and updated as part
> of the documentation that goes with this series.
>
> Hope this helps improve the understanding of this feature,

Yes, I think this is helpful.

> Table of Contents
> =================
> 1 Problem Statement
> 2 Solution: Opportunistic suspend
> 2.1 When to use a suspend blocker
> 2.2 Usage in PM aware drivers
>
>
> 1 Problem Statement
> ~~~~~~~~~~~~~~~~~~~~
>
> Want to to hit deep power state, even when the system is not actually
> idle.
>
> Why?
>
> - some hardware is not capable of deep power states in idle
> - difficulty getting userspace and/or kernel to be idle
>
> 2 Solution: Opportunistic suspend
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Create an additional "idle path" which has new rules for determining
> idleness. When this new "idle" is reached, trigger full-system
> suspend. Since a suspend is triggered whenever the opportunity
> arises, this is called opportunistic suspend.
>
> The new rules for making the idleness decision are simple:
>
> 1. system may suspend if and only if no suspend blockers are held
>
> 2.1 When to use a suspend blocker
> ==================================
>
> [A list of reasons why suspend blockers might be used would be very
> helpful here.]
>
> - ensure wakeup events propagate to userspace (e.g. keypad example in doc)
>
> - screen is on
>
> - someone mentioned "Google use cases"
> (would be nice to hear about more of these)

Yes, I think the Android developers know quite a few cases where suspend
blockers are useful.

> 2.2 Usage in PM aware drivers
> ==============================
>
> [An example of how a driver already using runtime PM would use
> a suspend blocker would also be helpful.

When we have any drivers using both in the tree, they will be used as examples
here.

Thanks,
Rafael


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