On Thu, Oct 26, 2017 at 10:35:39AM +1030, Andrew Jeffery wrote: > On Wed, 2017-10-25 at 09:14 +0100, Charles Keepax wrote: > > On Fri, Oct 20, 2017 at 07:32:53PM +1030, Andrew Jeffery wrote: > > > On Fri, 2017-10-20 at 09:27 +0200, Linus Walleij wrote: > > > > I don't see it as helpful to give userspace control over whether the line > > > > is persistent or not. It is more reasonable to assume persistance for > > > > userspace use cases, don't you think? Whether the system goes to sleep > > > > or the gpiochip resets should not make a door suddenly close or the > > > > lights in the christmas tree go out, right? I think if the gpiochip supports > > > > persistance of any kind, we should try to use it and not have userspace > > > > provide flags for that. > > > > > > Right. I guess the counter argument to your examples is if the gpio is > > > controlling any active process that we don't want to continue if we've > > > lost the capacity to monitor some other inputs (some kind of dead-man's > > > switch). But maybe the argument is that should be implemented in the > > > kernel anyway? > > > > > > > To me it certainly feels like decisions like this should live in > > the kernel, your talking about things that could cause very weird > > hardware behaviour if set wrong, so it makes sense to me to have > > that responsibility guarded in the kernel. > > I feel that taking this argument to its logical conclusion leads to > never exporting any GPIOs to userspace and doing everything in the > kernel. If userspace has exported the GPIO and is managing its state, > then it can *already* cause very weird hardware behaviour if set wrong. > The fact that userspace is controlling the GPIO state and not the > kernel already says that the kernel doesn't know how to manage it, so > why not expose the option for userspace to set the persistence, given > that it should know what it's doing? Admittedly yes, I guess it really comes down to use-cases. There are fairly strong use-cases to control GPIOs from user-space that justify the risks. The use-cases for being able to set non-persistent GPIOs from user-space seem less clear to me, but if they exist I certainly don't have any objection. Thanks, Charles -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
