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

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Date:	Wed, 19 Jan 2011 17:04:18 +0800
From:	"Dong, Chuanxiao" <chuanxiao.dong@...el.com>
To:	"Tardy, Pierre" <pierre.tardy@...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

Hi Pierre,
I think the runtime pm should not have any dependency with clock gating. Even the MMC driver won't clock gate SD/MMC card, host controller should still enter runtime suspend state, right?
So if auto suspended delay could be changed by user, then we can use pm_suspend_schedule to specify the latency which is longer than 8 clock cycle.

Thanks
Chuanxiao
> -----Original Message-----
> From: Tardy, Pierre
> Sent: Wednesday, January 19, 2011 12:39 AM
> To: Dong, Chuanxiao; linux-mmc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org; cjb@...top.org; 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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