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

[Christian König]

Adding Andrey as well.

Am 01.12.21 um 12:37 schrieb Yu, Lang:
> [SNIP]
>>>>>>> +	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?
> As far as I know, they usually use a HDT to collect information.
> And they request a hang when error occurred in ticket.
> "Suggested error responses include pop-up windows (by x86 driver, if this is possible) or simply hanging after logging the error."

In that case I suggest to set the "don't_touch_the_hardware_any_more" 
procedure we also use in case of PCIe hotplug.

Andrey has the details but essentially it stops the driver from touching 
the hardware any more, signals all fences and unblocks everything.

It should then be trivial to inspect the hardware state and see what's 
going on, but the system will keep stable at least for SSH access.

Might be a good idea to have that mode for other fault cases like page 
faults and hardware crashes.

Regards,
Christian.

>
> Regards,
> Lang
>