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

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Date:	Sun, 22 Mar 2015 14:59:27 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Alim Akhtar <alim.akhtar@...il.com>
Cc:	Jaehoon Chung <jh80.chung@...sung.com>,
	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

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.

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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