On 06/25/2013 08:32 AM, Linus Walleij wrote: > On Fri, Jun 21, 2013 at 11:17 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: >> On 06/20/2013 05:57 AM, Christian Ruppert wrote: > >> The Linux pinctrl subsystem specifically doesn't provide mutual >> exclusion between "mux function" and GPIO usage within a pin group, >> although perhaps a driver could internally. > > It used to block this at one point. But it doesn't make sense > when the hardware looks like so: > >>> +- SPI >>> Physical pins --- GPIO --- pinctrl -+- I2C >>> +- mmc > > As in this case it is perfectly legal to enable the GPIO as > input while the I2C bus is running and "spy" on the signals. > > The driver should probably not allow the GPIO output to be > driven while some peripheral is muxed in though, that could be > disastrous... Well, in the HW diagram above, GPIO output probably simply overrides "mux function" output, so everything would work as requested. Whether it makes sense to request such an override is a policy question that pinctrl itself probably shouldn't decide. After all, what if there's a pin group containing 4 pins, which are used by the board as 2 GPIO and 2 I2C. pinctrl shouldn't disallow selecting GPIO on any pin in that pin group simply because I2C is selected on it; that fact doesn't necessarily mean that the selected mux function actually uses every single pin in the group. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
