"legacy" usb stack fixes

Scott Long scottl at samsco.org
Fri Sep 12 18:23:02 UTC 2008


Scott Long wrote:
> This is close to How Things Should Be.  Each umass target having its own
> SIM and bus is indeed wrong, but I'm not sure if it's correct for all
> USB controllers and buses to be under a single SIM.  What would be the
> most correct is for each physical USB controller/bus instance to have
> its own SIM instance.  I don't know if it's better to do the attachment
> in ehci/ohci/uhci controller drivers or in usb bus driver; up in the
> controller drivers is probably more correct.  I don't like this hack of
> attaching stuff in a SYSINIT.
> 
> Scott
> 
> 

Now that I've thought some on it, I'll go one step further and say that
registering a single SIM for multiple controller+bus instances in a
SYSINIT will be highly undesirable thing to do.  Since you have to
register a lock with the CAM when you register the SIM, you'll wind up
serializing all of the USB controllers under a single lock.  Or you'll
probably try something dangerous and tricky with dropping the new global
lock and picking up an individual lock, then swizzling locks in the
completion and event paths, with the result being rather unsatisfying
and unpleasant.  So I know that you'll do what you believe is correct,
but please take my advice on the matter anyways.

Scott


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