From mboxrd@z Thu Jan  1 00:00:00 1970
From: Georg Gast <georg@schorsch-tech.de>
Subject: Searching a Bug on Raspberry Pi
Date: Sat, 29 Jun 2013 22:14:45 +0200
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Hi there!

Currently i try to locate a bug in drivers/mmc/host/sdhci.c on 
RaspberryPi. I know it is not the mainline kernel...

Currently i use Kernel 3.8.13 and RT Patch 3.8.13-rt12 on the kernel 
found at git://github.com/raspberrypi/linux.git on branch rpi-3.8.y.

The bug shows up at booting and after 3 seconds of booting as it wants 
to mount the rootfs in a deadlock. as i compiled sdhci_bcm2708 as a 
module i can boot the kernel and system as i pushed the system to a usb 
stick. As far as good.

Now i try to find the bug, if the rootfs is on the sdcard. I narrowd the 
deadlock down to the following lines:

void sdhci_spin_lock_irqsave(struct sdhci_host *host,unsigned long *flags)
{
     return;
#ifdef CONFIG_PREEMPT
     if(enable_llm)
     {
         while(sdhci_locked)
         {
             preempt_schedule();
         }
         spin_lock_irqsave(&host->lock,*flags);
         disable_irq(host->irq);
         if(host->second_irq)
             disable_irq(host->second_irq);
         local_irq_enable();
     }
     else
#endif
         spin_lock_irqsave(&host->lock,*flags);
}

void sdhci_spin_unlock_irqrestore(struct sdhci_host *host,unsigned long 
flags)
{
     return;
#ifdef CONFIG_PREEMPT
     if(enable_llm)
     {
         local_irq_disable();
         if(host->second_irq)
             enable_irq(host->second_irq);
         enable_irq(host->irq);
     }
#endif
     spin_unlock_irqrestore(&host->lock,flags);
}

in drivers/mmc/host/sdhci.c . The both return statements are added by 
me. Now i can boot the RT Preempt kernel but it is for sure not the 
right fix.

My problem is, that i dont know how those both functions should work 
with the rt preempt patch.

What can you suggest me to fix that deadlock? I already bought the book 
"Linux Kernel Development" but i dont know how the kernel works exaktly 
with the PREEMPT patch. Can you point me to a site which shows how 
RTPREEMPT works in the irqsave/restore functions or can you please 
describe it to me?

Thank you
Georg