[PATCH] sound: emu10k1 - fix system hang with Audigy2 ZS Notebook PCMCIA card

[Jaroslav Franek <jarin.franek@post.cz>]

from: Jaroslav Franek

When the Linux kernel is compiled with CONFIG_DEBUG_SHIRQ=y,
the Soundblaster Audigy2 ZS Notebook PCMCIA card causes the
system hang during boot (udev stage) or when the card is hot-plug.
The CONFIG_DEBUG_SHIRQ flag is by default 'y' with all Fedora
kernels since 2.6.23. The problem was reported as
https://bugzilla.redhat.com/show_bug.cgi?id=326411

The issue was hunted down to the snd_emu10k1_create() routine:

/* pseudo-code */
snd_emu10k1_create(...) {
	...
	request_irq(... IRQF_SHARED ...) {
		register the irq handler
		#ifdef CONFIG_DEBUG_SHIRQ
		call the irq handler: snd_emu10k1_interrupt() {
			poll I/O port   // <---- !! system hangs
			...
		}
		#endif
	}
	...
	snd_emu10k1_cardbus_init(...) {
		initialize I/O ports
	}
	...
}

The early access to I/O port in the interrupt handler causes
the freeze. Obviously it is necessary to init the I/O ports
before accessing them. This patch moves the registration of
the irq handler after the initialization of the I/O ports.

Signed-off-by: Jaroslav Franek <jarin.franek@post.cz>
---
This is the patch against 2.6.26-rc5. Please give it proper flaming,
it is my first so I do not deserve much mercy ;).

--- a/sound/pci/emu10k1/emu10k1_main.c	2008-05-29 21:29:12.000000000 +0200
+++ b/sound/pci/emu10k1/emu10k1_main.c	2008-06-04 21:31:35.000000000 +0200
@@ -1818,13 +1818,6 @@ int __devinit snd_emu10k1_create(struct 
 	}
 	emu->port = pci_resource_start(pci, 0);
 
-	if (request_irq(pci->irq, snd_emu10k1_interrupt, IRQF_SHARED,
-			"EMU10K1", emu)) {
-		err = -EBUSY;
-		goto error;
-	}
-	emu->irq = pci->irq;
-
 	emu->max_cache_pages = max_cache_bytes >> PAGE_SHIFT;
 	if (snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, snd_dma_pci_data(pci),
 				32 * 1024, &emu->ptb_pages) < 0) {
@@ -1887,6 +1880,14 @@ int __devinit snd_emu10k1_create(struct 
 	emu->fx8010.etram_pages.area = NULL;
 	emu->fx8010.etram_pages.bytes = 0;
 
+	/* irq handler must be registered after I/O ports are activated */
+	if (request_irq(pci->irq, snd_emu10k1_interrupt, IRQF_SHARED,
+			"EMU10K1", emu)) {
+		err = -EBUSY;
+		goto error;
+	}
+	emu->irq = pci->irq;
+
 	/*
 	 *  Init to 0x02109204 :
 	 *  Clock accuracy    = 0     (1000ppm)