RE: [PATCH v1 1/3]mmc: implemented runtime pm for mmc host

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> 
> First case:  you want to stop the clock _to_ the _card_ when not talking
> to it.  That has nothing to do with power saving performed within the
> host controller.  This is for reducing power consumption by the _card_
> (and possibly by the clock generator).  The runtime PM stuff has no
> business here as the decision to gate the clock on the card require
> MMC/SD protocol knowledge.

Could not the mmcclock be a device on this own, and use rpm to manage its state?

> Second case: you want the _host_CONTROLLER_ to be shut down so it
> doesn't consume power by itself when idle.  This would be performed when
> case 1 has gated the clock, but not necessarily always. 
Agree with this, this is the idea of the my implementation.

> Here the
> runtime PM infrastructure could make some sense.
> 
> All host controllers can gate the card's clock, but not all of them can
> power themselves down.  And maybe there would be a case for keeping the
> clock to a SDIO card active while the host controller is powered down.

> Knowledge for gating the card's clock is in the core code and
> independent from the host controller.
But knowledge on *how* to gate the clock is in the host controller driver, and/or platform code.


Pierre
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