On 03/17/2017 12:55 PM, Sakari Ailus wrote: > Hi Russell, > > On 03/17/17 13:42, Russell King - ARM Linux wrote: >> On Tue, Mar 14, 2017 at 08:55:36AM +0100, Hans Verkuil wrote: >>> We're all very driver-development-driven, and userspace gets very little >>> attention in general. So before just throwing in the towel we should take >>> a good look at the reasons why there has been little or no development: is >>> it because of fundamental design defects, or because nobody paid attention >>> to it? >>> >>> I strongly suspect it is the latter. >>> >>> In addition, I suspect end-users of these complex devices don't really care >>> about a plugin: they want full control and won't typically use generic >>> applications. If they would need support for that, we'd have seen much more >>> interest. The main reason for having a plugin is to simplify testing and >>> if this is going to be used on cheap hobbyist devkits. >> >> I think you're looking at it with a programmers hat on, not a users hat. >> >> Are you really telling me that requiring users to 'su' to root, and then >> use media-ctl to manually configure the capture device is what most >> users "want" ? > > It depends on who the user is. I don't think anyone is suggesting a > regular end user is the user of all these APIs: it is either an > application tailored for that given device, a skilled user with his test > scripts or as suggested previously, a libv4l plugin knowing the device > or a generic library geared towards providing best effort service. The > last one of this list does not exist yet and the second last item > requires help. > > Typically this class of devices is simply not up to provide the level of > service you're requesting without additional user space control library > which is responsible for automatic white balance, exposure and focus. > > Making use of the full potential of the hardware requires using a more > expressive interface. That's what the kernel interface must provide. If > we decide to limit ourselves to a small sub-set of that potential on the > level of the kernel interface, we have made a wrong decision. It's as > simple as that. This is why the functionality (and which requires taking > a lot of policy decisions) belongs to the user space. We cannot have > multiple drivers providing multiple kernel interfaces for the same hardware. Right. With my Cisco hat on I can tell you that Cisco would want full low-level control. If the driver would limit us we would not be able to use it. Same with anyone who wants to put Android CameraHAL on top of a V4L2 driver: they would need full control. Some simplified interface would be unacceptable. > > That said, I'm not trying to provide an excuse for not having libraries > available to help the user to configure and control the device more or > less automatically even in terms of best effort. It's something that > does require attention, a lot more of it than it has received in recent > few years. Right. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
