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

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Date:	Tue, 18 Jan 2011 16:39:02 +0000
From:	"Tardy, Pierre" <pierre.tardy@...el.com>
To:	"Dong, Chuanxiao" <chuanxiao.dong@...el.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cjb@...top.org" <cjb@...top.org>,
	"ohad@...ery.com" <ohad@...ery.com>
Subject: RE: [PATCH v1 1/3]mmc: implemented runtime pm for mmc host

> > I'm also worried about this patch not taking in account the 8 clock cycles before
> > shutting down the clock, contrary to the clock gating fw.
> > If you power down hc, you will also gate the clock. So the sdio protocol might not be
> > strictly followed.
> As mmc spec said, 8 clock cycles is needed. That is right.
> But I think if we have set the auto suspended delay for host, runtime pm core could make sure host to
> wait at least the auto suspended delay before shutting down the power of the device. So if the auto
> suspended delay is longer than 8 clock cycles, the mmc protocol can be followed, right?
I disagree. You cannot enforce this. It depends on clock speed, that can vary with sdio cards. 
User can change the autosuspend delay to whatever he wants, it should just change performance, but not functionality.

Why don't you just take my clock gating version?
Its working well, I'm using this for 2 weeks, and follow the linux-mmc latest improvement.

Regards,
Pierre


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