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

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

On Tue, 31 Jul 2012, Sylwester Nawrocki wrote:

> 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...

Eventually, when the clock API is available - yes, the client would just 
call clk_enable() / clk_disable(). But for now isn't it host's job to do 
that? Or you want to add new API for that?

Thanks
Guennadi

> > 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.

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/