Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 25/08/15 23:46, Rafael J. Wysocki wrote:
> On 8/25/2015 11:37 AM, Jon Hunter wrote:

[snip]

>> Vinod, thinking about this some more, I am wondering if it is just
>> better to get rid of the suspend/resume callbacks and simply handling
>> the state in the runtime suspend/resume callbacks. I think that would be
>> safe too, because once the clock has been disabled, then who knows what
>> the context state will be.
> 
> One caveat here: system suspend may be invoked at any time, so you need
> to ensure that the device is properly suspended when that happens.
> 
> I believe you at least need a ->suspend callback for that.

Thanks, makes sense.

On a related note, I see a few drivers, including this DMA driver doing
the following in the driver ->remove callback.

    pm_runtime_disable(&pdev->dev);
        !pm_runtime_status_suspended(&pdev->dev))
            tegra_dma_runtime_suspend(&pdev->dev);

I understand that the code is trying to ensure that the device is
suspended regardless of whether rpm is enabled or not in the kernel
config. However, looking at the pm_runtime_status_suspended() function,
AFAICT, it will always return false above as the disable_depth will be
greater than 0. So I am concerned that the tegra_dma_runtime_suspend()
is called even when not needed? However, I could also be missing
something here.

Cheers
Jon