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 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.