On Tue, Feb 9, 2010 at 12:14 PM, Anton Vorontsov <avoront...@ru.mvista.com> wrote: > On Tue, Feb 09, 2010 at 10:28:15AM -0700, Grant Likely wrote: > [...] >> Rather than having a lock at the device tree data pointer level which >> mixes usage with potentially many other drivers; wouldn't it make more >> sense to use a mutex at the of_gc subsystem context? > > I don't think so. > > of_gc = np->data; > lock(of_gc); (or lock(devtree)) > <do something with of_gc> > > doesn't provide us what we need, i.e. it doesn't guarantee that > np->data (of_gc) is still alive. > > And here: > > lock(np->data); (or lock(devtree)) > of_gc = np->data; > lock(of_gc); > <do something with of_gc> > > The second lock becomes useless (unless you also refcount np->data > usage and can drop the devtree/np->data lock, and grab some other > kind of lock, e.g. mutex, but this is silly).
Okay, I'm convinced now. The model is wrong. struct of_gc does need to be a member of struct gpio_chip and conditionally compiled against CONFIG_OF_GPIO. This locking requirement is just too plain ugly, and dereferencing the np->data pointer in this way is dangerous (what if something that is not struct of_gc is stored there). Put of_gc into struct gpio_chip, and I'll completely support that approach. g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
