[PATCH V4 2/2] drm/vc4: v3d: add PM suspend/resume support

[Maíra Canal]

Hi Stefan,

On 10/8/24 13:05, Stefan Wahren wrote:
> Hi Maíra,
> 
> Am 08.10.24 um 15:49 schrieb Maíra Canal:
>> Hi Stefan,
>>
>> On 10/3/24 09:41, Stefan Wahren wrote:
>>> Add suspend/resume support for the VC4 V3D component in order
>>> to handle suspend to idle properly.
>>>
>>> Signed-off-by: Stefan Wahren <wahrenst at gmx.net>
>>> ---
>>>   drivers/gpu/drm/vc4/vc4_v3d.c | 7 +++----
>>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/vc4/vc4_v3d.c
>>> b/drivers/gpu/drm/vc4/vc4_v3d.c
>>> index 2423826c89eb..8057b06c1f16 100644
>>> --- a/drivers/gpu/drm/vc4/vc4_v3d.c
>>> +++ b/drivers/gpu/drm/vc4/vc4_v3d.c
>>> @@ -368,7 +368,6 @@ void vc4_v3d_bin_bo_put(struct vc4_dev *vc4)
>>>       mutex_unlock(&vc4->bin_bo_lock);
>>>   }
>>>
>>> -#ifdef CONFIG_PM
>>>   static int vc4_v3d_runtime_suspend(struct device *dev)
>>>   {
>>>       struct vc4_v3d *v3d = dev_get_drvdata(dev);
>>> @@ -397,7 +396,6 @@ static int vc4_v3d_runtime_resume(struct device
>>> *dev)
>>>
>>>       return 0;
>>>   }
>>> -#endif
>>>
>>>   int vc4_v3d_debugfs_init(struct drm_minor *minor)
>>>   {
>>> @@ -507,7 +505,8 @@ static void vc4_v3d_unbind(struct device *dev,
>>> struct device *master,
>>>   }
>>>
>>>   static const struct dev_pm_ops vc4_v3d_pm_ops = {
>>> -    SET_RUNTIME_PM_OPS(vc4_v3d_runtime_suspend,
>>> vc4_v3d_runtime_resume, NULL)
>>> +    RUNTIME_PM_OPS(vc4_v3d_runtime_suspend, vc4_v3d_runtime_resume,
>>> NULL)
>>> +    SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
>>> pm_runtime_force_resume)
>>
>> I have a question: How can we guarantee that no jobs are running when
>> the system is forced to suspend?
> Not sure what do you mean with job. userspace task or v3d job within the
> driver?

I mean a V3D job. See, when we submit a CL to the GPU, we only know when
it's done through a IRQ. I'm thinking in the case where:

1. We submitted a CL to the GPU
2. We suspend but the job wasn't ended yet

What happens to this job? Is the GPU going to be in a unstable state
when we resume?

> 
> Do you have something specific in mind.
> 
> Why is there a difference between runtime pm and system pm?
>
As far as I can see, for system PM, we need at least to suspend V3D in
a stable state, without any jobs running and with IRQs disabled.

Best Regards,
- Maíra

> I must confess that i didn't test a system sleep while running a v3d
> application.
> 
> Best regards
> Stefan
>>
>> Best Regards,
>> - Maíra
>>
>>>   };
>>>
>>>   static const struct component_ops vc4_v3d_ops = {
>>> @@ -538,6 +537,6 @@ struct platform_driver vc4_v3d_driver = {
>>>       .driver = {
>>>           .name = "vc4_v3d",
>>>           .of_match_table = vc4_v3d_dt_match,
>>> -        .pm = &vc4_v3d_pm_ops,
>>> +        .pm = pm_ptr(&vc4_v3d_pm_ops),
>>>       },
>>>   };
>>> -- 
>>> 2.34.1
>>>
>