From: AMEET M. PARANJAPE <aparanja@redhat.com>
Date: Wed, 7 Jan 2009 10:51:03 -0500
Subject: [ppc64] cell: axon-msi: Retry on missing interrupt
Message-id: 20090107155006.15465.76014.sendpatchset@squad5-lp1.lab.bos.redhat.com
O-Subject: [PATCH RHEL5.4 BZ472405 2/2] powerpc/cell/axon-msi: Retry on missing interrupt
Bugzilla: 472405
RH-Acked-by: David Howells <dhowells@redhat.com>

RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=472405

Description:
===========
The problem is that after a kexec, the MSIC hardware still points
into the middle of the old ring buffer. We set up the ring buffer
during reboot, but not the offset into it. On older kernels, this
would cause a storm of thousands of spurious interrupts after a
kexec, which would most of the time get dropped silently.

With the new code, we time out on each interrupt, waiting for
it to become valid. If more interrupts come in that we time
out on, this goes on indefinitely, which eventually leads to
a hard crash.

The solution in this patch is to read the current offset from
the MSIC when reinitializing it. This now works correctly, as
expected.

RHEL Version Found:
================
RHEL 5.3

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1639654

Upstream Status:
================
commit id is 23e0e8afafd9ac065d81506524adf3339584044b

Test Status:
============
the MSIC hardware still points into the middle of the old ring buffer. We set
up the ring buffer during reboot, but not the offset into it. On older kernels,
this would cause a storm of thousands of spurious interrupts after a
kexec, which would most of the time get dropped silently.

With this patch this behavior is not seen.
===============================================================
Ameet Paranjape 978-392-3903 ext 23903
IBM on-site partner

Proposed Patch:
===============

diff --git a/arch/powerpc/platforms/cell/axon_msi.c b/arch/powerpc/platforms/cell/axon_msi.c
index 9bbb406..a90d726 100644
--- a/arch/powerpc/platforms/cell/axon_msi.c
+++ b/arch/powerpc/platforms/cell/axon_msi.c
@@ -420,6 +420,9 @@ static int axon_msi_probe(struct of_device *device,
 			MSIC_CTRL_IRQ_ENABLE | MSIC_CTRL_ENABLE |
 			MSIC_CTRL_FIFO_SIZE);
 
+	msic->read_offset = msic_dcr_read(msic, MSIC_WRITE_OFFSET_REG)
+				& MSIC_FIFO_SIZE_MASK;
+
 	device->dev.platform_data = msic;
 
 	ppc_msi_md.setup_msi_irqs = axon_msi_setup_msi_irqs;