From bc294838cc3443a2fbec58f8936ad4bd0a0b3055 Mon Sep 17 00:00:00 2001
From: Sven Schnelle <svens@stackframe.org>
Date: Thu, 14 Oct 2021 21:49:16 +0200
Subject: parisc: add support for TOC (transfer of control)

Almost all PA-RISC machines have either a button that
is labeled with 'TOC' or a BMC function to trigger a TOC.
TOC is a non-maskable interrupt that is sent to the processor.
This can be used for diagnostic purposes like obtaining a
stack trace/register dump or to enter KDB/KGDB.

As an example, on my c8000, TOC can be used with:

CONFIG_KGDB=y
CONFIG_KGDB_KDB=y

and the 'kgdboc=ttyS0,115200' appended to the command line.

Press ^[( on serial console, which will enter the BMC command line,
and enter 'TOC s':

root@(none):/# (
cli>TOC s
Sending TOC/INIT.
<Cpu3> 2800035d03e00000  0000000040c21ac8  CC_ERR_CHECK_TOC
<Cpu0> 2800035d00e00000  0000000040c21ad0  CC_ERR_CHECK_TOC
<Cpu2> 2800035d02e00000  0000000040c21ac8  CC_ERR_CHECK_TOC
<Cpu1> 2800035d01e00000  0000000040c21ad0  CC_ERR_CHECK_TOC
<Cpu3> 37000f7303e00000  2000000000000000  CC_ERR_CPU_CHECK_SUMMARY
<Cpu0> 37000f7300e00000  2000000000000000  CC_ERR_CPU_CHECK_SUMMARY
<Cpu2> 37000f7302e00000  2000000000000000  CC_ERR_CPU_CHECK_SUMMARY
<Cpu1> 37000f7301e00000  2000000000000000  CC_ERR_CPU_CHECK_SUMMARY
<Cpu3> 4300100803e00000  c0000000001d26cc  CC_MC_BR_TO_OS_TOC
<Cpu0> 4300100800e00000  c0000000001d26cc  CC_MC_BR_TO_OS_TOC
<Cpu2> 4300100802e00000  c0000000001d26cc  CC_MC_BR_TO_OS_TOC
<Cpu1> 4300100801e00000  c0000000001d26cc  CC_MC_BR_TO_OS_TOC

Entering kdb (current=0x00000000411cef80, pid 0) on processor 0 due to NonMaskable Interrupt @ 0x40c21ad0
[0]kdb>

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>
---
 arch/parisc/Kconfig | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'arch/parisc/Kconfig')

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 906187a412ec..3296fcb90019 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -291,6 +291,20 @@ config SMP
 
 	  If you don't know what to do here, say N.
 
+config TOC
+	bool "Support TOC switch"
+	default y if 64BIT || !SMP
+	help
+	  Most PA-RISC machines have either a switch at the back of the machine
+	  or a command in BMC to trigger a TOC interrupt. If you say Y here a
+	  handler will be installed which will either show a backtrace on all
+	  CPUs, or enter a possible configured debugger like kgdb/kdb.
+
+	  Note that with this option enabled, the kernel will use an additional 16KB
+	  per possible CPU as a special stack for the TOC handler.
+
+	  If you don't want to debug the Kernel, say N.
+
 config PARISC_CPU_TOPOLOGY
 	bool "Support cpu topology definition"
 	depends on SMP
-- 
cgit