linux-kernel - Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc

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Date:	Fri, 21 Nov 2014 21:29:58 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>,
	addy ke <addy.ke@...k-chips.com>
Cc:	Doug Anderson <dianders@...omium.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"tgih.jun@...sung.com" <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Chris Ball <chris@...ntf.net>,
	Dinh Nguyen <dinguyen@...era.com>,
	Heiko Stübner <heiko@...ech.de>,
	Olof Johansson <olof@...om.net>,
	Sonny Rao <sonnyrao@...omium.org>,
	Alexandru Stan <amstan@...omium.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-rockchip@...ts.infradead.org,
	"zhenfu.fang" <zhenfu.fang@...k-chips.com>,
	Eddie Cai <cf@...k-chips.com>, lintao <lintao@...k-chips.com>,
	chenfen <chenfen@...k-chips.com>, zyf <zyf@...k-chips.com>,
	Jianqun Xu <xjq@...k-chips.com>,
	Tao Huang <huangtao@...k-chips.com>,
	Chris Zhong <zyw@...k-chips.com>,
	姚智情 <yzq@...k-chips.com>,
	han jiang <hj@...k-chips.com>,
	Kever Yang <kever.yang@...k-chips.com>,
	zhangqing <zhangqing@...k-chips.com>,
	Lin Huang <hl@...k-chips.com>
Subject: Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for
 vqmmc

On 11/21/2014 09:06 PM, Ulf Hansson wrote:
> [...]
> 
>> Sure
>> If the first card is sd2.0 since startup, dw_mci_switch_voltage will not be called,
> 
> That can't be right. mmc_power_up() should trigger
> dw_mci_switch_voltage() to be invoked.

Since dw_mci_switch_voltage() is invoked, voltage is changed from 1.8v to 2.7v (minimum value 2.7-3.6v), isn't?

> 
>> and card can be identified. But if UHS card is pulgged in first, the vqmmc will be down to 1.8v.
>>
>> when sd2.0 card is pulgged in, mmc core will call dw_mci_switch_voltage to change vqmmc to 3.3v
>> (MMC_SINGLE_VOTAGE_330). So vqmmc will be set 2.7v, if we request 2.7-3.6v.
>>
>> But vmmc is always 3.3v,becuase it be set min_volt = max_volt = 3.3v in dt tables.

vmmc is fixed voltage?

>>
>> So the result:
>> vmmc = 3.3v and vqmmc = 2.7v, and sd2.0 card is failed to identify in my test.
> 
> Hmm. I wonder why it works the first time? Could it be that your
> regulator have voltage ramp up time that isn't properly considered?

if oscilloscope can use, can we know more exactly?

Best Regards,
Jaehoon Chung
> 
> Kind regards
> Uffe
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