On Mon, May 12, 2014 at 07:43:22PM +0200, Laurent Pinchart wrote:

> The problem is not limited to IOMMUs. We have similar dependencies at 
> suspend/resume time with camera interfaces for instance, where two completely 
> unrelated device in the Linux device hierarchy (a camera interface platform 
> device in the SoC and an I2C camera sensor) need to be suspended and resumed 
> in a controlled order. I'm sure many more use cases exist.

> Whether we can (partly) reuse existing infrastructure for this is not clear. 
> I'd like to gather use cases, to first find out exactly how widespread the 
> need is, and whether we can come up with a common solution or we are really 
> faced with different classes of similarly looking but distinct issues.

This is something ASoC has been resolving since forever with the machine
drivers, Russell King recently created a generic version of the code
that does the dependency deferral glue (see linux/component.h).  It's
not a model of elegance but it ends up getting the job done.

Anyway, I'm definitely interested in this - a couple of the subsystems I
maintain are affected and it's something I've thought about a bit.