Re: [PATCH/RESEND] soc-camera: add runtime pm support for subdevices

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Hans Verkuil wrote:
>> Hans Verkuil wrote:

>>> But if you have ideas to improve the core to make it easier to add pm
>>> support to the drivers that need it, then I am all for it.
>> IMO, the runtime pm should be supported at V4L core, but some callbacks
>> are
>> needed. Also, I can see some classes of PM at the core:
>>
>> 	TV standard demod and sensors only need to be powerup when streaming.
> 
> Definitely not the demod: that's generally used to detect whether there is
> a TV signal and what audio format is used. You want that also when not
> streaming. I guess it can be powered down though when no files are open.

This is device-specific: on some devices, the tuner provides the info (and
even decode the audio carrier). Also, on some modes (e. g. radio), the demod 
may be turned off.

>> So, I think that we'll need some callbacks to the drivers, in order to do
>> the
>> power management on the applicable components. The final action should be
>> at
>> the driver level, but supported by the core.
> 
> I guess the essential information is:
> 
> 1) is someone using the driver (i.e. is a device node open, which is not
> necessarily limited to v4l2-type device nodes)?
> 2) are we actively streaming from or to some particular input or output?
> 
> And we probably need some easy way to detect and set the powersaving state
> for each component (subdev or the main v4l2_device).

krefs can be a good alternative to check device usage and enable powersaving,
but we'll need some callbacks to save/restore chip register values per dev/subdev.
> 
> I really need to research the pm stuff...
> 
> Regards,
> 
>          Hans
> 
>>> Regards,
>>>
>>>         Hans
>>>
>>>> Thanks
>>>> Guennadi
>>>> ---
>>>> Guennadi Liakhovetski, Ph.D.
>>>> Freelance Open-Source Software Developer
>>>> http://www.open-technology.de/
>>>>
>>>
>>
>> --
>>
>> Cheers,
>> Mauro
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> 
> 


-- 

Cheers,
Mauro