On Tue, Sep 09, 2014 at 06:26:27PM +0000, Rajat Jain wrote: > Hi, > > I'm not a newbie, but I am trying to understand the semantics of deferred > probing. > > My question is generic, but for an example: > > Let's say I have a platform driver "A" for a device "a", that requires device > "b" (controlled by driver "B") to be operational first. Both A &B can be > built as part of kernel, or as modules independently. As far as I could > tell, there is no way to specify the ORDER in which the drivers' probe > routines should be called. I took a look at modprobe / depmod, but it seems > to be of relevance for modules only that are loaded from user space. My > questions: > > 1) Is there a way to specify that "Kernel should call A's probe routine only > after B's probe routine"?
You can ask module A to load the required module B. For example, lib/textsearch.c:textsearch_prepare -> lookup_ts_algo lookup_ts_algo will load ts_bm.ko/ts_fsm.ko/ts_kmp.ko as required. > > 2) How I currently do this: In A's probe routine, I currently check if the > device "b" is available. If not, I return -EPROBE_DEFER. This mostly works > ok. However, I'm curious about the case where the driver B is not built as > part of the kernel but A is. After getting an _EPROB_DEFER from a B's probe > routine, when will the kernel try again? And for how long would it keep on > trying? I verified that if I load the driver B manually from user space, the > A's probe routine does not get called (if it gets called now - it would have > returned success!). > > Thanks, > > Rajat > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies