Re: [PATCH] [media] uapi/media.h: Use u32 for the number of graph objects

Arnd Bergmann
2015-12-17T15:20:34Z

On Thursday 17 December 2015 12:58:06 Mauro Carvalho Chehab wrote:
> > Can you clarify how the 'topology_version' is used here? Is that
> > the version of the structure layout that decides how we interpret the
> > rest, or is it a number that is runtime dependent?
>
> No, topology_version is just a mononotonic counter that starts on 0
> and it is incremented every time a graph object is added or removed.
>
> It is meant to be used to track if the topology changes after a previous
> call to this ioctl.
>
> On existing media controller embedded device hardware, it should
> always be zero, but on devices that allow dynamic hardware changes
> (some embedded DTV hardware allows that - also on devices with FPGA,
> with RISC CPUs or hot-pluggable devices) should use it to know if the
> hardware got modified.
>
> This is also needed on multi-function devices where different drivers
> are used for each function. That's the case of au0828, with uses a
> media driver for video, and the standard USB Audio Class driver for
> audio. As the drivers are independent, the topology_version will
> be zero when the first driver is loaded, but it will change during
> at probe time on second driver. It will also be increased if one
> of the drivers got unbind.

Ok, got it. Thanks for the explanation.

Arnd