linux-kernel - Re: [PATCH v4 1/3] mmc: dw_mmc: update clock after host reach a stable voltage

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Date:	Wed, 25 Feb 2015 13:05:13 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Alim Akhtar <alim.akhtar@...il.com>
Cc:	Addy Ke <addy.ke@...k-chips.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Heiko Stübner <heiko@...ech.de>,
	Eddie Cai <cf@...k-chips.com>, lintao <lintao@...k-chips.com>,
	Tao Huang <huangtao@...k-chips.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Subject: Re: [PATCH v4 1/3] mmc: dw_mmc: update clock after host reach a
 stable voltage

Alim,

On Tue, Feb 24, 2015 at 11:52 PM, Alim Akhtar <alim.akhtar@...il.com> wrote:
>>> This looks a HACK to me.
>>> If stabilizing host voltage regulator is the problem, can you try out
>>> below patch, and see if this resolve your issue?
>>
>> Actually, IMHO Alim's patch is more of a hack than Addy's.  There's
>> already a 10ms delay between "power up" and "power on" in the MMC core
>> in mmc_power_up() state.  That delay is commented as:
>>
> Well, my suggestion (adding 5ms in switch_volatge) was based on DW_MMC
> databook (V2.41a) section "7.4.1.2 Voltage switch Normal Scenario"
> step #7 which says:" After the 5ms timer expires, the host voltage
> regulator is stable".

So all of that should be handled by the core.  Just reading the DW_MMC
databook can be confusing because they don't differentiate between
what's in the SDMMC spec and what's DW_MMC specific.

Check out mmc_set_signal_voltage(), specifically:

* During a signal voltage level switch, the clock must be gated
* for 5 ms according to the SD spec

-Doug
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