cx23885: risc op code error - strange solution...

Commit Message

Raimonds Cicans June 17, 2021, 8:30 p.m. UTC

Hi!

Yet again I try to fight cx23885 driver's "risc op code error" bug.

I found very weird "fix":
If I apply attached patch _AND_ enable KASAN, then problem disappear.
If I disable KASAN or delete _ANY_ new line from patch, then problem 
reappear.

I tried to replace "printk" with delays and with memory barriers, but 
nothing works.

I would like to hear from community any ideas:
1. why this "fix" helps
2. what weird things "printk" can do when KASAN enabled
3. why we need two consecutive "cx23885_irq_get_mask(dev);" commands, 
first of which need strange "companions"
4. what else I can try to use instead of "printk"


Raimonds Cicans

Patch

--- /usr/src/linux-5.10.27-gentoo__orig/drivers/media/pci/cx23885/cx23885-core.c	2021-04-03 09:20:56.609971911 +0300
+++ /usr/src/linux-5.10.27-gentoo/drivers/media/pci/cx23885/cx23885-core.c	2021-06-17 22:34:49.503333355 +0300
@@ -1517,6 +1517,10 @@ 
 	if (debug > 4)
 		cx23885_tsport_reg_dump(port);
 
+	printk(KERN_INFO);
+	cx23885_irq_get_mask(dev);
+	printk(KERN_INFO);
+
 	cx23885_irq_get_mask(dev);
 
 	/* clear dma in progress */