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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sylwester,

On Tuesday 31 July 2012 15:28:52 Sylwester Nawrocki wrote:
> On 07/31/2012 02:59 PM, Guennadi Liakhovetski wrote:
> > 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?
> 
> Indeed, looking at existing drivers, the clocks' handling is now mostly
> done in the host drivers. Only the omap3isp appears to do the right thing,
> i.e. delegating control over the clock to client drivers, but it does it
> with platform_data callbacks.
> 
> We've already discussed adding a new API for that,
> http://www.mail-archive.com/linux-media@vger.kernel.org/msg35359.html
> 
> However using common clock API and binding a clock to client device
> (either DT based or not) sounds like a best approach to me.
> 
> Waiting for the common clock API to be generally available maybe we
> could add some clock ops at the v4l2_device ? Just a humble suggestion,
> I'm not sure whether it is really good and needed or not.

I'm fine with that (or something similar) as an interim solution.

-- 
Regards,

Laurent Pinchart