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

From: Jiaxun Yang
Date: Thu Sep 17 2020 - 10:57:05 EST

在 2020/9/17 20:41, Jinyang He 写道:
Hi, Huacai,

On 09/16/2020 01:39 PM, Huacai Chen wrote:
Hi, Jinyang,

On Tue, Sep 15, 2020 at 10:17 PM Jinyang He <hejinyang@xxxxxxxxxxx> wrote:

On 09/16/2020 09:33 AM, Jiaxun Yang wrote:
于 2020年9月15日 GMT+08:00 下午9:07:43, Jinyang He <hejinyang@xxxxxxxxxxx> 写到:
Add loongson_kexec_prepare(), loongson_kexec_shutdown() and
loongson_kexec_crashdown() for passing the parameters of kexec_args.

To start loongson64, CPU0 needs 3 parameters:
fw_arg0: the number of cmd.
fw_arg1: cmd structure which seems strange, the cmd array[index]'s
          value is cmd string's address, index >= 1.
fw_arg2: environment.

Secondary CPUs do not need parameter at once. They query their
mailbox to get PC, SP and GP in a loop before CPU0 brings them up
and passes these parameters via mailbox.

loongson_kexec_prepare(): Alloc new memory to save cmd for kexec.
Combine the kexec append option string as cmd structure, and the cmd
struct will be parsed in fw_init_cmdline() of arch/mips/fw/lib/cmdline.c.
image->control_code_page need pointing to a safe memory page. In order to
maintain compatibility for the old firmware the low 2MB is reserverd
and safe for Loongson. So let it points here.

loongson_kexec_shutdown(): Wake up all present CPUs and let them go
to reboot_code_buffer. Pass the kexec parameters to kexec_args.

loongson_crash_shutdown(): Pass the kdump parameters to kexec_args.

The assembly part provide a way like BIOS doing to keep secondary
CPUs in a querying loop.

This patch referenced [1][2][3].

[1] arch/mips/cavium-octeon/setup.c

Co-developed-by: Youling Tang <tangyouling@xxxxxxxxxxx>
Signed-off-by: Youling Tang <tangyouling@xxxxxxxxxxx>
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
arch/mips/kernel/relocate_kernel.S | 19 ++++++++
arch/mips/loongson64/reset.c       | 88 ++++++++++++++++++++++++++++++++++++++
2 files changed, 107 insertions(+)

diff --git a/arch/mips/kernel/relocate_kernel.S b/arch/mips/kernel/relocate_kernel.S
index ac87089..061cbfb 100644
--- a/arch/mips/kernel/relocate_kernel.S
+++ b/arch/mips/kernel/relocate_kernel.S
@@ -133,6 +133,25 @@ LEAF(kexec_smp_wait)
+#define MAILBOX_BASE 0x900000003ff01000
Please avoid hardcoded SMP information. You're breaking Loongson 3B support.

Ok, I see. Since my machine is Loongson 3A. I'll send v2
after I test it in 3B.
1, My original version can work on both Loongson-3A and Loongson-3B,
why you modify my patch and hadn't discuss with me?

2, With this single patch both kexec and kdump cannot work reliably,
because kexec need this patch:

    and kdump need my first patch in my original version:

    You may argue that you have tested. Yes, I believe that, I'm not
saying that you haven't test, and I'm not saying that your patch
cannot work, I'm just saying that your patch is not robust.

3, I'm the original author and paying attention to kexec/kdump
continuosly, I will send a new version once the above two patches be
accepted. But you re-send my patch without any communication with me,
why you so impatient?


1, Your original version:

This patch can work on Loongson-3A, I tested it.

But it works wrong after the follow behaviors,
   kexec -l vmlinux --append=cmdline_kexec
   kexec -p vmlinux --append=cmdline_kdump
   kexec -e

It works but cmdline_kdump merged cmdline_kexec.

And this patch memcpy from fw_arg2 to kexec_envp and later memcpy from
kexec_envp to fw_arg2 when fw_arg2 was not changed, it's redundant.

However, I have not Loongson-3B now, and did not test it. For this patch,
does it work well on Loongson-3B3000/Loongson-3B4000?

Hi Jingyang,

Well for Loongson-3B I meant 3B1000/3B1500, which have different layout
of SMP registers. For 3B3000/3B4000 everyone know they're just different
branding to the same silicon.

3, I try to fix Loongson64 kexec function since I joined the community.
I fell sorry to not do enough research on Loongson64 kexec. My first patch:

I'm glad to see Loongson staff joining the community and enhance our code.
It is common practice to investigate historical changes before do something
to the upstream code :-)

It fixed problem about "Crash kernel" which can be traced back to linux-5.4.
At that time, I thought there is no developer work on Kexec. Thus, I did a
lot on Kexec. Are you really continuosly paying attention to kexec/kdump?
With the exploring and developing deep, I found your patch several days ago
after I did a draft patch witch referenced:

There is no doubt that your patch gives me confidence and suggestion while
it gives me worry. As a newcomer, I do not know if should communicate with
you since your patch was committed one year ago. And now it may be a good
chance to do some communication.

You should *always* try to *credit* others properly, that's the first thing.
Communication is optional but highly recommanded.

Recently I can smell there are some tensions raised between the community and
the Loongson company, mainly about GPL violation and Loongson's attitude
towards the community. Personaly I don't hold any hostility to Loongosn's
practice in the community but I'd also like to see Loongson show their respect
to the community.


- Jiaxun


- Jinyang.