Re: [PATCH] drm/amdgpu: add support to SMU debug option

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Am 01.12.21 um 12:20 schrieb Yu, Lang:
[AMD Official Use Only]

-----Original Message-----
From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
Sent: Wednesday, December 1, 2021 6:49 PM
To: Yu, Lang <Lang.Yu@xxxxxxx>; Koenig, Christian
<Christian.Koenig@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Lazar, Lijo
<Lijo.Lazar@xxxxxxx>; Huang, Ray <Ray.Huang@xxxxxxx>
Subject: Re: [PATCH] drm/amdgpu: add support to SMU debug option

Am 01.12.21 um 11:44 schrieb Yu, Lang:
[AMD Official Use Only]



-----Original Message-----
From: Koenig, Christian <Christian.Koenig@xxxxxxx>
Sent: Wednesday, December 1, 2021 5:30 PM
To: Yu, Lang <Lang.Yu@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Lazar, Lijo
<Lijo.Lazar@xxxxxxx>; Huang, Ray <Ray.Huang@xxxxxxx>
Subject: Re: [PATCH] drm/amdgpu: add support to SMU debug option

Am 01.12.21 um 10:24 schrieb Lang Yu:
To maintain system error state when SMU errors occurred, which will
aid in debugging SMU firmware issues, add SMU debug option support.

It can be enabled or disabled via amdgpu_smu_debug debugfs file.
When enabled, it makes SMU errors fatal.
It is disabled by default.

== Command Guide ==

1, enable SMU debug option

    # echo 1 > /sys/kernel/debug/dri/0/amdgpu_smu_debug

2, disable SMU debug option

    # echo 0 > /sys/kernel/debug/dri/0/amdgpu_smu_debug

v3:
    - Use debugfs_create_bool().(Christian)
    - Put variable into smu_context struct.
    - Don't resend command when timeout.

v2:
    - Resend command when timeout.(Lijo)
    - Use debugfs file instead of module parameter.

Signed-off-by: Lang Yu <lang.yu@xxxxxxx>
Well the debugfs part looks really nice and clean now, but one more
comment below.

---
    drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c        | 3 +++
    drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h            | 5 +++++
    drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c | 2 ++
    drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c             | 8 +++++++-
    4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
index 164d6a9e9fbb..86cd888c7822 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
@@ -1618,6 +1618,9 @@ int amdgpu_debugfs_init(struct amdgpu_device
*adev)
    	if (!debugfs_initialized())
    		return 0;

+	debugfs_create_bool("amdgpu_smu_debug", 0600, root,
+				  &adev->smu.smu_debug_mode);
+
    	ent = debugfs_create_file("amdgpu_preempt_ib", 0600, root, adev,
    				  &fops_ib_preempt);
    	if (IS_ERR(ent)) {
diff --git a/drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h
b/drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h
index f738f7dc20c9..50dbf5594a9d 100644
--- a/drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h
+++ b/drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h
@@ -569,6 +569,11 @@ struct smu_context
    	struct smu_user_dpm_profile user_dpm_profile;

    	struct stb_context stb_context;
+	/*
+	 * When enabled, it makes SMU errors fatal.
+	 * (0 = disabled (default), 1 = enabled)
+	 */
+	bool smu_debug_mode;
    };

    struct i2c_adapter;
diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
b/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
index 6e781cee8bb6..d3797a2d6451 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
@@ -1919,6 +1919,8 @@ static int aldebaran_mode2_reset(struct
smu_context *smu)
    out:
    	mutex_unlock(&smu->message_lock);

+	BUG_ON(unlikely(smu->smu_debug_mode) && ret);
+
    	return ret;
    }

diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c
b/drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c
index 048ca1673863..9be005eb4241 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c
@@ -349,15 +349,21 @@ int smu_cmn_send_smc_msg_with_param(struct
smu_context *smu,
    		__smu_cmn_reg_print_error(smu, reg, index, param, msg);
    		goto Out;
    	}
+
    	__smu_cmn_send_msg(smu, (uint16_t) index, param);
    	reg = __smu_cmn_poll_stat(smu);
    	res = __smu_cmn_reg2errno(smu, reg);
-	if (res != 0)
+	if (res != 0) {
    		__smu_cmn_reg_print_error(smu, reg, index, param, msg);
+		goto Out;
+	}
    	if (read_arg)
    		smu_cmn_read_arg(smu, read_arg);
    Out:
    	mutex_unlock(&smu->message_lock);
+
+	BUG_ON(unlikely(smu->smu_debug_mode) && res);
BUG_ON() really crashes the kernel and is only allowed if we prevent
further data corruption with that.

Most of the time WARN_ON() is more appropriate, but I can't fully
judge here since I don't know the SMU code well enough.
This is what SMU FW guys want. They want "user-visible (potentially fatal)
errors", then a hang.
They want to keep system state since the error occurred.
Well that is rather problematic.

First of all we need to really justify that, crashing the kernel is not something
easily done.

Then this isn't really effective here. What happens is that you crash the kernel
thread of the currently executing process, but it is perfectly possible that another
thread still tries to send messages to the SMU. You need to have the BUG_ON()
before dropping the lock to make sure that this really gets the driver stuck in the
current state.
Thanks. I got it. I just thought it is a kenel panic.
Could we use a panic() here?

Potentially, but that might reboot the system automatically which is probably not what you want either.

How does the SMU firmware team gather the necessary information when a problem occurs?

When they connect external hardware a BUG_ON() while holding the SMU lock might work, but if they want to SSH into the system you should probably rather set a flag that the hardware shouldn't be touched any more by the driver and continue.

Otherwise the box is most likely really unstable after this.

Regards,
Christian.


Regards,
Lang

Regards,
Christian.

Regards,
Lang

Christian.

+
    	return res;
    }





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