linux-kernel - RE: MMC: Card detection through pin CD/DAT3 issue

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Date:	Wed, 19 Mar 2008 09:41:14 +0100
From:	"Wappler Marcel" <Marcel.Wappler@...dgeco.net>
To:	<7eggert@....de>, "Pierre Ossman" <drzeus-mmc@...eus.cx>,
	<linux-kernel@...r.kernel.org>
Subject: RE: MMC: Card detection through pin CD/DAT3 issue

Thank you, Pierre,

this special host controller is more an SDHCI _inspired_ than a
_compliant_ one. Not only powering off the card bus led to the not
working card detection but also the RESET_ALL function. Both
tasks are reqired by the SDHCI standard after removing the card.
But Pierre has prepared the sdhci.c very well: there is a quirk
called "SSM_QUIRK_NO_CARD_NO_RESET". In combination with disabling
power off after a card removal now it works.

Bodo Eggert wrote:
>> I have found this requirement in the SD host controller spec:
>> "The card detect is active regardless of the SD Bus Power."
>> 
>> I wonder how the card should be able to pull up the CD/DAT3 Pad to
>> VCC if its only VCC pad is not connected to VCC due to the fact that
>> the host controller has switched off the cards power - any idea how
>> this could be managed?

> If the VCC pin is connected to 0 V, the "pullup" will pull 
> down to 0V. 
> If the controller reverses it's logic while VCC=0, it might work.

I am concerned  that in this case there would be neither a pull 
up nor a pull down at this signal. Due to floating gates that input
could lead to millions of "card detection" events a second, if
no card is inserted?

Regards,
Marcel

Marcel Wappler
Bridgeco AG
CH-8600 Dübendorf
Switzerland
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