Re: [RFC] MMC: Proposals on reworking clock and power management

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On Thu, Oct 28, 2010 at 9:43 PM, Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
> On Thu, 28 Oct 2010, Ohad Ben-Cohen wrote:
>
>> On Thu, Oct 28, 2010 at 5:39 PM, Kishore Kadiyala
>> <kishorek.kadiyala@xxxxxxxxx> wrote:
>> > Wouldn't adapting the host driver just to PM-Runtime will answer the
>> > above issues?
>>
>> It's not enough.
>>
>> When the card is runtime suspended, sure, the host controller will
>> immediately get idle notification by runtime PM core.
>>
>> But you may still want to gate the clock to the host controller on bus
>> inactivity, even if the card is not runtime suspended. The decision to
>> do this should come from the mmc core.
>
> This is not clear that this is something that the core can effectively
> help with.  Opportunistic power saving at the host controller level is
> pretty much hardware dependent and may wildly vary in capabilities...
> and bugs.  So in this later case I think the driver for the host
> controller is the best place to just set up a timer and gate the clock
> after a certain period of inactivity for example.

Agree,
So briefly, calling pm_runtime_put_sync using a activity based timer
in the host Controller
driver will gate the clock to the controller .
On idle notification to PM runtime core, which will trigger a call to
the runtime_suspend hook in bus.c
[https://patchwork.kernel.org/patch/226671/ ] which will perform
powering off the Card

Regards,
Kishore
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