Re: [RFC] move sensor control out of kernel

[Paulius Zaleckas <paulius.zaleckas@teltonika.lt>]

eric miao wrote:
>>  > The benefits I can think of now are:
>>  >
>>  > 1. simplified sensor driver design
>>
>>  It is pretty simple with soc-camera framework also. And the best thing
>>  is that it is unified. If you implement sensor driver in userspace then
>>  what kind of interface should V4L data bus driver expose.
>>
> 
> The soc-camera is pretty good. Yet it doesn't solve the issue of
> complicated sensor control. mt9m001.c and mt9v022.c are two
> good examples, but are all too simple. I have a sensor driver here
> with more than 4000 lines of code.

Yes I can imagine driver for analog devices ADV family video decoder :)
Some time ago I wrote driver for ADV...

But I don't imagine application or library with support for all 
devices... Kernel is easy to configure and to compile only drivers you 
need. Also kernel modules are good to load only the driver you need.

Another thing is that there will be different multiple implementations 
of this "4000 lines of code" driver. This means that each of them will 
be tested less than the single one in kernel.

>>  > Another biggest concern to the V4L2 API itself, sensor nowadays has
>>  > more control ability than it used to be, some smart sensor provides
>>  > even more like auto focus control, lens control, flash mode, and many
>>  > other features that current V4L2 API cannot cover.
>>
>>  Implement these controls. Make a patch and send it here. If everything
>>  is OK it should be merged and V4L will be capable to handle these controls.
>>
> 
> Mmm...then do you expect an API growing into a monster in the kernel space?

I guess this will happen anyway, because of tv tuners, dvb-t cards and 
etc. There is no way there to separate "sensor" from the data bus.

And you will have to export data bus interface to the userspace.

>>  My conclusion: your idea just moves problem from kernel to userspace,
>>  but doesn't solve it...
>>
> 
> I'm not trying to solve how to control the sensor but how to simplify
> the kernel effort and maybe with small reward of stability and ease
> of development.

I must agree about kernel stability here.

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