[RFC] [patch 5/6] powerpc 2.6.20-rt8: fix a boot error for handle_percpu_irq

  To fix the following boot time error by removing ack member added by
the rt patch.

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Processor 1 found.
Brought up 2 CPUs
------------[ cut here ]------------
kernel BUG at arch/powerpc/platforms/cell/interrupt.c:86!
pu 0x1: Vector: 700 (Program Check) at [c00000000fff3c80]
    pc: c000000000033f9c: .iic_eoi+0x58/0x64
    lr: c00000000009add8: .handle_percpu_irq+0xd4/0xf4
    sp: c00000000fff3f00
   msr: 9000000000021032
  current = 0xc000000000fee040
  paca    = 0xc000000000509e80
    pid   = 0, comm = swapper
kernel BUG at arch/powerpc/platforms/cell/interrupt.c:86!
enter ? for help
[link register   ] c00000000009add8 .handle_percpu_irq+0xd4/0xf4
[c00000000fff3f00] c00000000009ada8 .handle_percpu_irq+0xa4/0xf4 (unreliable)
[c00000000fff3f90] c000000000023bb8 .call_handle_irq+0x1c/0x2c
[c000000000ff7950] c00000000000c910 .do_IRQ+0xf8/0x1b8
[c000000000ff79f0] c000000000034f34 .cbe_system_reset_exception+0x74/0xb4
[c000000000ff7a70] c000000000022610 .system_reset_exception+0x40/0xe0
[c000000000ff7af0] c000000000003378 system_reset_common+0xf8/0x100

--- Exception: 100 (System Reset) at c000000000035008 .cbe_power_save+0x94/0xb0

[c000000000ff7e70] c000000000012030 .cpu_idle+0xc8/0x144
[c000000000ff7f00] c000000000026894 .start_secondary+0x150/0x174
[c000000000ff7f90] c000000000008364 .start_secondary_prolog+0xc/0x10
1:mon>

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  I found a pile of e-mail started by Sergei Shtylyov on linuxppc-dev regarding this.
    Subject: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi type IRQ handlers
    From: Sergei Shtylyov [off-list ref]
    Date: Sun, 19 Nov 2006 22:43:34 +0300

  Though I don't quite get the conclusion, the code does not work at least
on celleb when handle_percpu_irq is applied.  Since the handle_percpu_irq calls
both .ask and .eoi and when ask is set to iic_eoi, then iic_eoi() is called twice
for one interrupt.  It hits BUG_ON(iic->eoi_ptr < 0)!

  Anthor workaround could be to add one more irq_chip structure for handle_percpu_irq
which does not have ack member...

  Any comments?

Signed-off-by: Tsutomu Owa <redacted>
-- owa

diff -rup linux-rt8/arch/powerpc/platforms/cell/interrupt.c rt/arch/powerpc/platforms/cell/interrupt.c

--- linux-rt8/arch/powerpc/platforms/cell/interrupt.c	2007-02-20 14:30:38.000000000 +0900
+++ rt/arch/powerpc/platforms/cell/interrupt.c	2007-03-02 18:48:52.000000000 +0900

@@ -90,7 +90,6 @@ static struct irq_chip iic_chip = {
 	.typename = " CELL-IIC ",
 	.mask = iic_mask,
 	.unmask = iic_unmask,
-	.ack = iic_eoi,
 	.eoi = iic_eoi,
 };