Hi Guennadi, On Mon, Oct 08, 2012 at 02:23:25PM +0200, Guennadi Liakhovetski wrote: ... > If we do it from the bridge driver, we could install an I2C bus-notifier, > _before_ the subdevice driver is probed, i.e. upon the > BUS_NOTIFY_BIND_DRIVER event we could turn on the clock. If subdevice > probing was successful, we can then wait for the BUS_NOTIFY_BOUND_DRIVER > event to switch the clock back off. BUT - if the subdevice fails probing? > How do we find out about that and turn the clock back off? There is no > notification event for that... Possible solutions: > > 1. timer - ugly and unreliable. > 2. add a "probing failed" notifier event to the device core - would this > be accepted? > 3. let the subdevice turn the master clock on and off for the duration of > probing. > > My vote goes for (3). Ideally this should be done using the generic clock > framework. But can we really expect all drivers and platforms to switch to > it quickly enough? If not, we need a V4L2-specific callback from subdevice > drivers to bridge drivers to turn the clock on and off. That's what I've > done "temporarily" in this patch series for soc-camera. I'd say the clock has to be controlled by the sub-device driver. Sensors also have a power-up (and power-down) sequences that should be followed. Usually they also involve switching the external clock on (and off) at a given point of time. Also the OMAP 3 provides that clock through ISP so it, too, requires the generic clock framework to function with DT. > Suppose we decide to do the same for V4L2 centrally - add call-backs. Then I'd prefer to use the generic clock framework, albeit I admit it may take some time till all the relevant platforms support it. Nevertheless, if there's going to be a temporary solution it should be removed once the clock framework support is there. Kind regards, -- Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
