Re: [RFC 3/3] drm/amd: Return -EBUSY for amdgpu_pmops_thaw() on success

["Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>]

On 10/20/2025 1:50 PM, Rafael J. Wysocki wrote:
> On Mon, Oct 20, 2025 at 8:32 PM Mario Limonciello (AMD) (kernel.org)
> <superm1@kernel.org> wrote:
>>
>>
>>
>> On 10/20/2025 12:39 PM, Rafael J. Wysocki wrote:
>>> On Mon, Oct 20, 2025 at 7:28 PM Mario Limonciello (AMD) (kernel.org)
>>> <superm1@kernel.org> wrote:
>>>>
>>>>
>>>>
>>>> On 10/20/2025 12:21 PM, Rafael J. Wysocki wrote:
>>>>> On Mon, Oct 20, 2025 at 6:53 PM Mario Limonciello (AMD)
>>>>> <superm1@kernel.org> wrote:
>>>>>>
>>>>>> From: Mario Limonciello <mario.limonciello@amd.com>
>>>>>>
>>>>>> The PM core should be notified that thaw was skipped for the device
>>>>>> so that if it's tried to be resumed (such as an aborted hibernate)
>>>>>> that it gets another chance to resume.
>>>>>>
>>>>>> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
>>>>>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 2 +-
>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> index 61268aa82df4d..d40af069f24dd 100644
>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>> @@ -2681,7 +2681,7 @@ static int amdgpu_pmops_thaw(struct device *dev)
>>>>>>
>>>>>>            /* do not resume device if it's normal hibernation */
>>>>>>            if (!pm_hibernate_is_recovering() && !pm_hibernation_mode_is_suspend())
>>>>>> -               return 0;
>>>>>> +               return -EBUSY;
>>>>>
>>>>> So that's why you need the special handling of -EBUSY in the previous patch.
>>>>
>>>> Yup.
>>>>
>>>>>
>>>>> I think that you need to save some state in this driver and then use
>>>>> it in subsequent callbacks instead of hacking the core to do what you
>>>>> want.
>>>>>
>>>>
>>>> The problem is the core decides "what" to call and more importantly
>>>> "when" to call it.
>>>>
>>>> IE if the core thinks that something is thawed it will never call
>>>> resume, and that's why you end up in a bad place with Muhammad's
>>>> cancellation series and why I proposed this one to discuss.
>>>>
>>>> We could obviously go back to dropping this case entirely:
>>>>
>>>> if (!pm_hibernate_is_recovering() && !pm_hibernation_mode_is_suspend())
>>>>
>>>> But then the display turns on at thaw(), you do an unnecessary resource
>>>> eviction, it takes a lot longer if you have a ton of VRAM etc.
>>>
>>> The cancellation series is at odds with this code path AFAICS because
>>> what if hibernation is canceled after the entire thaw transition?
>>
>> Muhammad - did you test that specific timing of cancelling the hibernate?
>>>
>>> Some cleanup would need to be done before thawing user space I suppose.
>>
>> I agree; I think that series would need changes for it.
>>
>> But if you put that series aside, I think this one still has some merit
>> on it's own.  If another driver aborted the hibernate, I think the same
>> thing could happen if it happened to run before amdgpu's device thaw().
>>
>> That series just exposed a very "easy" way to reproduce this issue.
> 
> Device thaw errors don't abort anything AFAICS.
> 

You're right; it doesn't abort, it just is saved to the logs.
The state is also not maintained.
> What can happen though is that another device may abort the final
> "power off" transition, which is one of the reasons why I think that
> rolling it back is generally hard.

That's exactly the reason for the first patch in this series.  The state 
of whether it succeeded isn't recorded.  So if thaw non-fatally fails 
and you've saved state to indicate this then any of the other calls that 
run can try again.