linux-kernel - Re: mmc select voltage functionality

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Date:	Mon, 26 Nov 2007 18:46:17 +0100
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	Madhusudhan C <madhu_lkml@...oo.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: mmc select voltage functionality

On Thu, 22 Nov 2007 05:34:11 -0800 (PST)
Madhusudhan C <madhu_lkml@...oo.com> wrote:

> Hi Pierre,
> 
> I have a question on the mmc_select_voltage fn of the mmc core file drivers/mmc/core/core.c.
> 
> During the power up sequence the mmc_power_up fn sets the OCR bit to setup 3V. Subsequentely the mmc_select_voltage fn selects the lowest voltage
> the card can support.The host->ios.power_mode is not changed to MMC_POWER_UP before calling mmc_set_ios from this function hence the power_mode remains in MMC_POWER_ON state.So my question is, how should the controller driver handle this change in volatge. Under which case of power mode should the controller driver change the voltage again when a dual voltage card is detected?
> 

To be completely correct, the MMC layer should probably power down the card first, yes. Right now most drivers will handle all of these things as they see fit. Haven't seen a single bug report about it yet so...

Just change the voltage in whatever way makes sense for your controller.

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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