hysteresis for CAM_RESRC_UNAVAIL

[Ade Lovett]

On Sep 26, 2006, at 15:13 , Scott Long wrote:
> I think the intent here was to have some sort of an asynchronous  
> "resource is now available" and "I'm no longer busy" mechanism,  
> maybe via an AC_ message.  However, a think that the timeout that  
> you're proposing is much better than the vacuum that is there now.

Definitely the goal should be towards an async notification mechanism.

In the meantime, rather than hard-coding half a second, could we have  
the timeout be a sysctl for easier experimentation as to what an  
"appropriate" value would be? (defaulting to 500ms)  Gives a few  
extra options to tinker with things if a suitably degenerate case can  
be found with which to exercise this code, rather than having to  
recompile the kernel.  Providing progressively longer delays on  
repeated calls to cam_periph_error() seems to be somewhat non-trivial  
since it's going to require maintaining extra state.

-aDe