linux-kernel - Re: [PATCH] mmc: rtsx: add card power off during probe

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Date:	Mon, 22 Sep 2014 10:09:32 +0000
From:	Roger Tseng <rogerable@...ltek.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
CC:	micky <micky_ching@...lsil.com.cn>, Chris Ball <chris@...ntf.net>,
	"Samuel Ortiz" <sameo@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Wei_wang <wei_wang@...lsil.com.cn>
Subject: Re: [PATCH] mmc: rtsx: add card power off during probe

On Thu, 2014-09-18 at 23:14 +0200, Ulf Hansson wrote:
> [...]
> 
> >>
> >> In that case, don't forget to enable MMC_CAP2_FULL_PWR_CYCLE.
> >>
> >> >
> >> > if MMC_CAP2_NO_PRESCAN_POWERUP enable, will call mmc_power_off() at start,
> >> > then it will check ios.power_mode, but the state is MMC_POWER_OFF and just
> >> > return.
> >>
> >> Uhh, that's right! So, I wonder why we invokes mmc_power_off() from
> >> that path at all.
> >>
> >> Hmm, I think we should change the behavior in mmc_start_host(), like below:
> >> 1) Add a "MMC_POWER_UNDEFINED" state which is what the power state
> >> should be assigned to at allocation.
> >> 2 ) From mmc_start_host(), invoke mmc_power_off() when
> >> MMC_CAP2_NO_PRESCAN_POWERUP and MMC_CAP2_FULL_PWR_CYCLE is set.
> >>
> >> Would that work?
> > Yes. I have confirmed this by following changes. The MMC_POWER_UNDEFINED
> > designation in mmc_start_host() will eventually cause a power-off
> > operation.
> >
> > But I wonder if we need to additionally check MMC_CAP2_FULL_PWR_CYCLE
> > before calling mmc_power_off()?
> 
> The intent from my side was to keep the current behaviour for those
> that already used MMC_CAP2_NO_PRESCAN_POWERUP, but it's s not a big
> deal.
> 

I checked the log and found the commit that invokes mmc_power_off():
a08b17be8b984a7c51cd5a480cd977363df353f9
0d3e3350d5871c53464be4c92d57198744247005
(https://www.mail-archive.com/linux-mmc@vger.kernel.org/msg19638.html )

The proposed change might bring back some delay since invoking
mmc_power_off() in mmc_start_host() is more than NOP now and triggers
real power-off and re-init in sdhci.

Will this be OK?

> So, let's try your proposal, thus don't check MMC_CAP2_FULL_PWR_CYCLE.
> 
> Can you repost new version of your patches and please split them up on
> core and host separately.
> 
> Kind regards
> Uffe
> 
> ------Please consider the environment before printing this e-mail.

-- 
Best regards,
Roger Tseng