Re: [RFC/PATCH 09/13] media: s5k6aa: Add support for device tree based instantiation

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

On 07/31/2012 02:26 PM, Guennadi Liakhovetski wrote:
>>>> But should we allow host probe() to succeed if the sensor isn't present ?
>>>
>>> I think we should, yes. The host hardware is there and functional -
>>> whether or not all or some of the clients are failing. Theoretically
>>> clients can also be hot-plugged. Whether and how many video device nodes
>>> we create, that's a different question.
>>
>> I think I can agree with you on this (although I could change my mind if this 
>> architecture turns out to result in unsolvable technical issues). That will 
>> involve a lot of work though.
> 
> There's however at least one more gotcha that occurs to me with this 
> approach: if clients fail to probe, how do we find out about that and turn 
> clocks back off? One improvement to turning clocks on immediately in 

Hmm, wouldn't it be the client that turns a clock on/off when needed ?
I'd like to preserve this functionality, so client drivers can have
full control on the power up/down sequences. While we are trying to
improve the current situation...

> host's probe() is to only do it in a BUS_NOTIFY_BIND_DRIVER notifier. But 
> how do we find out, that probing failed? No notifier is called in this 
> case. We could use a time-out, but that's ugly. I think, we could ever 
> request a new notifier for this case. We could also require client drivers 
> to call a V4L2 function in this case, but that's not very pretty either.

--

Regards,
Sylwester