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Message-ID: <49C9E4B8.3000708@gmail.com>
Date: Wed, 25 Mar 2009 09:00:56 +0100
From: =?UTF-8?B?Sm9zw6kgTWFyw63CrWEgRmVybsOhbmRleiBHb256w6FsZXo=?= 
	<josemariafg@gmail.com>
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To: Pierre Ossman <drzeus-list@drzeus.cx>
CC: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] mmc: Some microSD cards are not recognized by PCIxx12
 SDA controller
References: <49B5C091.3090303@gmail.com> <20090324211748.30cd7429@mjolnir.ossman.eu>
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Pierre Ossman wrote:
> On Tue, 10 Mar 2009 02:21:21 +0100
>> diff -Nrpu linux-2.6.28.5/drivers/mmc/core/core.c.orig linux-2.6.28.5/drivers/mmc/core/core.c
>> --- linux-2.6.28.5/drivers/mmc/core/core.c.orig	2009-03-10 01:30:19.000000000 +0100
>> +++ linux-2.6.28.5/drivers/mmc/core/core.c	2009-03-10 01:29:44.000000000 +0100
>> @@ -514,7 +514,7 @@ static void mmc_power_up(struct mmc_host
>>  	 * This delay should be sufficient to allow the power supply
>>  	 * to reach the minimum voltage.
>>  	 */
>> -	mmc_delay(2);
>> +	mmc_delay(10);
>>  
> 
> A delay of 10 is just enough to trigger a sleep on most kernels
> (HZ=100). Have you determined the lower bound of these two values?
> 

Well, I have been using the patch in a kernel with HZ=300, tickless (CONFIG_NO_HZ) and desktop preemption (CONFIG_PREEMPT_VOLUNTARY), but I didn't determine the lower bound. As I explained in the patch at -mm tree, I took as base the patch:

http://list.drzeus.cx/pipermail/sdhci-devel/2007-December/002089.html

and I only extrapolated the need for a higher delay just after MMC_POWER_UP to this one and after MMC_POWER_ON. When I was looking for a fix for the problem I was suffering with my microSD card and laptop, I remember I found some e-mails from two years ago pointing out to some change in the scheduler which uncovered the problem.

As I'm going to install 2.6.29 today, I can test the patch with it and HZ=100.
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