linux-kernel - Re: [PATCH 5/6] Unified AVR32/AT91 MCI Driver Support for a VCC Pin

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Date:	Mon, 15 Jun 2009 11:17:36 -0700
From:	Rob Emanuele <poorarm@...reis.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>,
	Andrew Victor <avictor.za@...il.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, drzeus-mmc@...eus.cx
Subject: Re: [PATCH 5/6] Unified AVR32/AT91 MCI Driver Support for a VCC Pin

Nicolas,

On Mon, Jun 15, 2009 at 9:20 AM, Nicolas Ferre<nicolas.ferre@...el.com> wrote:
> Rob Emanuele :
>> Add support to the atmel-mci driver for a VCC pin in order to conserve
>> power if the MMC interface is powered down.
>
> Can you elaborate a bit more. In particular, I do not understand the
> concept of "vcc_pin_act_low".
>

Like the original at91_mci driver, this patch adds the ability to use
a pin to toggle 3.3V power going to the SD Card.  In my case the pin
is tied to a International Rectifier 6420 P-type MOSFET since a port
pin alone cannot drive the SD Card.  When I pull the vcc_pin low, 3.3V
can reach the SD Card to power it.  The "vcc_pin_act_low" (pin active
low) determines which way the pin should be pulled to enable power to
the SD Card.  If vcc_pin_act_low is true, when the card needs to get
powered up, it sets the vcc_pin low.  Other board designs may need a
pin driven high to power the SD Card.

Thanks,

Rob
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