[alsa-devel] Backported sbxfi driver, possible fix

[Thomas Scheunemann]

I think I found a bug in the driver, which at least for me was
responsible for the crashes with pulseaudio.

A little backstory:

I have a Fedora 8 System with an SB X-Fi installed and of course
no sound. I didn't want to replace the entire ALSA driver, so I
just took the files sbxfi.c and emu20k1-regs.h from the unstable
sources, wrote a small spec-file and am now at a point where I
can just "rpm -i" the driver as a dkms package and just modprobe
the driver.

After that "speaker-test -D hw -c 2 -r 96000 -t sine" works just
fine, but as soon as pulseaudio is started my System froze.

The bug I think I found is in the get_xfi_order function. As long
as pages actually is a power of two it works correctly. But if
pages isn't a power of two it should round up, but it rounds down.
As a result I believe this screws up sbxfi_alloc_tlb_pages.

After a small modification to get_xfi_order:

--- /tmp/sbxfi.c	2008-10-25 14:51:55.000000000 +0200
+++ sbxfi.c	2008-10-25 14:03:48.000000000 +0200
@@ -851,11 +851,12 @@
 /* get the order of pages (power-of-two) */
 static int get_xfi_order(unsigned int pages)
 {
-	int order = -1;
-	do {
+	int order = 0;
+	pages--;
+	while(pages){
 		pages >>= 1;
 		order++;
-	} while (pages);
+	}
 	return order;
 }
 
the driver started working with pulseaudio, it doesn't crash, and I
even get sound though it still is a bit distorted.