linux-kernel - Re: [PATCH] mmc: dw_mmc: Don't send clock off command if power is off

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Date:	Fri, 27 Mar 2015 16:21:09 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>,
	Alim Akhtar <alim.akhtar@...il.com>
Cc:	Seungwon Jeon <tgih.jun@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Addy Ke <addy.ke@...k-chips.com>,
	Alexandru Stan <amstan@...omium.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Chris Ball <chris@...ntf.net>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: dw_mmc: Don't send clock off command if power is off

Hi,

On 03/23/2015 06:59 AM, Doug Anderson wrote:
> Alim,
> 
> On Sun, Mar 22, 2015 at 5:16 AM, Alim Akhtar <alim.akhtar@...il.com> wrote:
>>>         case MMC_POWER_OFF:
>>> -               /* Turn clock off before power goes down */
>>> -               dw_mci_setup_bus(slot, false);
>>> +               /* Turn clock off before power goes down; only if powered */
>>> +               if (slot->host->vqmmc_enabled)
>>> +                       dw_mci_setup_bus(slot, false);
>>>
>> vqmmc_enabled is always _true_ when entering MMC_POWER_OFF case..right?
>> Is this done for extra protection? Or do you have a case where vqmmc
>> is OFF and driver still calls dw_mci_setup_bus from here?
> 
> Hmm.  I know I got it into the debugger in at least one reboot case
> where it was failing to turn the clock off.  I thought I confirmed it
> was the core trying to call MMC_POWER_OFF when the power was already
> off, but now I'm less certain.  I looked back at my debug session and
> I don't see where I got that evidence.  :-/  Certainly if I put a
> printout here right now I can't see my code making a difference.

I'm not sure this is really needs...and i can't find any error case..

Best Regards,
Jaehoon Chung
> 
> Unfortunately the crash was a very rare one, so I may have to go back
> to the drawing board here...
> 
> -Doug
> 

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