PROBLEM: Linux 3.6.2 fails to boot on IBM Cell

[Grant Likely]

On Thu, Oct 18, 2012 at 10:59 PM, Dennis Schridde <devurandom at gmx.net> wrote:
> Am Donnerstag, 18. Oktober 2012, 22:32:55 schrieb Grant Likely:
>> Unfortunately the debug messages don't show up in the console log by
>> default. Can you either send the output of 'dmesg' after booting, or
>> add "loglevel=8" to the kernel boot parameters?
> Here you go.
>
> I also see some lines like:
> irq: no irq domain found for /axon at 10000000000/plb5/pciex-utl at a00000a000004000
> Is that also a problem?

[cc'ing linuxppc-dev]

Okay, so what is happening is that the function cbe_init_pm_irq() is
trying to set up hwirq numbers 0x7e, 0x17e, 0x27e and continuing up
every 0x100 to 0xff7e. This happens because that function is
calculating the hwirq number used for_each_node, and shifts the node
number up 8 bits to make up the upper bits of the hwirq number.
However, according the the header file, only '0' and '1' are actual
valid values for the upper bits.

CONFIG_NODES_SHIFT = 8 for PowerPC 64, which accounts for the range 0..0xff.

arch/powerpc/platforms/cell/interrupt.h defines the values of
IIC_IRQ_NODE_SHIFT = 8 and IIC_IRQ_NODE_MASK 0x100.

So, from the context, I assume the function is trying to set up a PM
interrupt for each CPU in the Cell processor; and that there are 2 of
them. for_each_node() knows nothing of this and dutifully tries to set
up the irq for 256 processors; way beyond what is valid for the irq
controller.

Also, it should be noted that the irq does actually get set up by
irqdomain.c, but because everything above 0x1ff is larger than the
lookup table, it complains. The new code complains loudly (as you
discovered) if someone tries to use a hwirq larger than the map where
the old code didn't.

Looks to me like the fix is to change for_each_node() to something as
simple as "for (i = 0; i < 2; i++)"

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.