Re: [PATCH V3] MIPS: Loongson64: Add kexec/kdump support

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Fri, Jan 08, 2021 at 06:07:39PM +0800, Jinyang He wrote:
> Unlike the cavium-octeon platform, the Loongson64 platform needs some
> changes. Before the kernel starts, (before entering the kernel_entry), each
> CPU has its own state (the SMP system). For Loongson64, only the boot CPU
> will enter the kernel_entry, and other CPUs will query their mailbox value
> in a loop. This is what the BIOS does for the CPU. Here is different from
> cavium-octeon. All CPUs will enter the kernel_entry on cavium-octeon
> platform. Then the kernel_entry_setup, the co-CPUs will enter the query
> loop. I saw the kernel_entry_setup of other platforms, such as ip27, malta,
> and generic. They are not like cavium-octeon and the co-CPUs entering the
> loop may be earlier than entering kernel_entry. So I have reason to guess
> that most SMP system platform CPUs are similar to Loongson64.
> 
> relocate_kernel.S is like BIOS doing s omething for the CPU. It allows the
> boot CPU to start from the new kernel_entry and makes the co-CPUs enter a
> loop. The already existing infrastructure may be more suitable for non-smp
> platforms. Although we can do something with plat_smp_ops.kexec_nonboot_cpu,
> more new problems will arise in that case. The kexec process actually runs
> on a copy of relocate_kernel.S, which will bring a lot of problems...
> 
> Above all just my personal thoughts.

thank you for describing current state. So it looks like kexec and SMP
is probably only working for Octeon and maybe some MIPS VPE based SMP
systems, but not with "real" cores.

How about the patch below as preparation for your loongson64 kexec patch ?
You only need to put write a kexec_smp_wait_final macro and the rest of
your patch stays the same...

Thomas.


From 81d3e1e24a0dae48f310b8d819d625f88139ef9b Mon Sep 17 00:00:00 2001
From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Date: Tue, 19 Jan 2021 21:58:55 +0100
Subject: [PATCH] MIPS: Use macro for kexec_smp_wait specials

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
 .../include/asm/mach-cavium-octeon/kernel-entry-init.h   | 8 ++++++++
 arch/mips/kernel/relocate_kernel.S                       | 9 ++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/mips/include/asm/mach-cavium-octeon/kernel-entry-init.h b/arch/mips/include/asm/mach-cavium-octeon/kernel-entry-init.h
index c38b38ce5a3d..b071a7353ee1 100644
--- a/arch/mips/include/asm/mach-cavium-octeon/kernel-entry-init.h
+++ b/arch/mips/include/asm/mach-cavium-octeon/kernel-entry-init.h
@@ -157,4 +157,12 @@
 	.macro	smp_slave_setup
 	.endm
 
+#define USE_KEXEC_SMP_WAIT_FINAL
+	.macro  kexec_smp_wait_final
+	.set push
+	.set noreorder
+	synci		0($0)
+	.set pop
+	.endm
+
 #endif /* __ASM_MACH_CAVIUM_OCTEON_KERNEL_ENTRY_H */
diff --git a/arch/mips/kernel/relocate_kernel.S b/arch/mips/kernel/relocate_kernel.S
index ac870893ba2d..f3c908abdbb8 100644
--- a/arch/mips/kernel/relocate_kernel.S
+++ b/arch/mips/kernel/relocate_kernel.S
@@ -11,6 +11,8 @@
 #include <asm/stackframe.h>
 #include <asm/addrspace.h>
 
+#include <kernel-entry-init.h>
+
 LEAF(relocate_new_kernel)
 	PTR_L a0,	arg0
 	PTR_L a1,	arg1
@@ -125,11 +127,8 @@ LEAF(kexec_smp_wait)
 1:	LONG_L		s0, (t0)
 	bne		s0, zero,1b
 
-#ifdef CONFIG_CPU_CAVIUM_OCTEON
-	.set push
-	.set noreorder
-	synci		0($0)
-	.set pop
+#ifdef USE_KEXEC_SMP_WAIT_FINAL
+	kexec_smp_wait_final
 #else
 	sync
 #endif
-- 
2.29.2


-- 
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good idea.                                                [ RFC1925, 2.3 ]