[2/2] drm/msm: Add support for GPU cooling

[Akhil P Oommen]

On 10/13/2020 11:10 PM, mka at chromium.org wrote:
> On Tue, Oct 13, 2020 at 07:23:34PM +0530, Akhil P Oommen wrote:
>> On 10/12/2020 11:10 PM, mka at chromium.org wrote:
>>> On Mon, Oct 12, 2020 at 07:03:51PM +0530, Akhil P Oommen wrote:
>>>> On 10/10/2020 12:06 AM, mka at chromium.org wrote:
>>>>> Hi Akhil,
>>>>>
>>>>> On Thu, Oct 08, 2020 at 10:39:07PM +0530, Akhil P Oommen wrote:
>>>>>> Register GPU as a devfreq cooling device so that it can be passively
>>>>>> cooled by the thermal framework.
>>>>>>
>>>>>> Signed-off-by: Akhil P Oommen <akhilpo at codeaurora.org>
>>>>>> ---
>>>>>>     drivers/gpu/drm/msm/msm_gpu.c | 13 ++++++++++++-
>>>>>>     drivers/gpu/drm/msm/msm_gpu.h |  2 ++
>>>>>>     2 files changed, 14 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
>>>>>> index 55d1648..93ffd66 100644
>>>>>> --- a/drivers/gpu/drm/msm/msm_gpu.c
>>>>>> +++ b/drivers/gpu/drm/msm/msm_gpu.c
>>>>>> @@ -14,6 +14,7 @@
>>>>>>     #include <generated/utsrelease.h>
>>>>>>     #include <linux/string_helpers.h>
>>>>>>     #include <linux/devfreq.h>
>>>>>> +#include <linux/devfreq_cooling.h>
>>>>>>     #include <linux/devcoredump.h>
>>>>>>     #include <linux/sched/task.h>
>>>>>> @@ -107,9 +108,18 @@ static void msm_devfreq_init(struct msm_gpu *gpu)
>>>>>>     	if (IS_ERR(gpu->devfreq.devfreq)) {
>>>>>>     		DRM_DEV_ERROR(&gpu->pdev->dev, "Couldn't initialize GPU devfreq\n");
>>>>>>     		gpu->devfreq.devfreq = NULL;
>>>>>> +		return;
>>>>>>     	}
>>>>>>     	devfreq_suspend_device(gpu->devfreq.devfreq);
>>>>>> +
>>>>>> +	gpu->cooling = of_devfreq_cooling_register(gpu->pdev->dev.of_node,
>>>>>> +			gpu->devfreq.devfreq);
>>>>>> +	if (IS_ERR(gpu->cooling)) {
>>>>>> +		DRM_DEV_ERROR(&gpu->pdev->dev,
>>>>>> +				"Couldn't register GPU cooling device\n");
>>>>>> +		gpu->cooling = NULL;
>>>>>> +	}
>>>>>>     }
>>>>>>     static int enable_pwrrail(struct msm_gpu *gpu)
>>>>>> @@ -926,7 +936,6 @@ int msm_gpu_init(struct drm_device *drm, struct platform_device *pdev,
>>>>>>     	msm_devfreq_init(gpu);
>>>>>> -
>> Will remove this unintended change.
>>>>>>     	gpu->aspace = gpu->funcs->create_address_space(gpu, pdev);
>>>>>>     	if (gpu->aspace == NULL)
>>>>>> @@ -1005,4 +1014,6 @@ void msm_gpu_cleanup(struct msm_gpu *gpu)
>>>>>>     		gpu->aspace->mmu->funcs->detach(gpu->aspace->mmu);
>>>>>>     		msm_gem_address_space_put(gpu->aspace);
>>>>>>     	}
>>>>>> +
>>>>>> +	devfreq_cooling_unregister(gpu->cooling);
>>>>>
>>>>> Resources should be released in reverse order, otherwise the cooling device
>>>>> could use resources that have already been freed.
>>>>> Why do you think this is not the correct order? If you are thinking
>>>> about devfreq struct, it is managed device resource.
>>>
>>> I did not check specifically if changing the frequency really uses any of the
>>> resources that are released previously, In any case it's not a good idea to
>>> allow other parts of the kernel to use a half initialized/torn down device.
>>> Even if it isn't a problem today someone could change the driver to use any
>>> of these resources (or add a new one) in a frequency change, without even
>>> thinking about the cooling device, just (rightfully) asuming that things are
>>> set up and torn down in a sane order.
>> 'sane order' relative to what specifically here? Should we worry about freq
>> change at this point because we have already disabled gpu runtime pm and
>> devfreq?
> 
> GPU runtime PM and the devfreq being disabled is not evident from the context
> of the function. You are probably right that it's not a problem in practice,
> but why give reason for doubts in the first place if this could be avoided
> by following a common practice?
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> 
Other option I see is to create a managed device resource (devm) version 
of the devfreq_cooling_register API and use that. Is that what you are 
trying to suggest?

-Akhil.