On Tue, Dec 2, 2014 at 5:12 PM, Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Dec 02, 2014 at 03:29:46PM +0100, Linus Walleij wrote: >> On Tue, Dec 2, 2014 at 3:13 PM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote: >> > On Tue, Dec 2, 2014 at 1:36 AM, Maxime Ripard >> > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: >> >> >> The only thing I'd like to have would be that the request here would >> >> be non-exclusive, so that a later driver would still be allowed later >> >> on to request that GPIO later on and manage it itself (ideally using >> >> the usual gpiod_request function). >> > >> > Actually we have a plan (and I have some code too) to allow multiple >> > consumers per GPIO. Although like Benoit I wonder why you would want >> > to hog a GPIO and then request it properly later. Also, that probably >> > means we should abandon the hog since it actively drives the line and >> > would interfere with the late requested. How to do that correctly is >> > not really clear to me. >> >> I don't get the usecase. A hogged GPIO is per definition hogged. >> This sounds more like "initial settings" or something, which is another >> usecase altogether. > > We do have one board where we have a pin (let's say GPIO14 of the bank > A) that enables a regulator that will provide VCC the bank B. > > Now, both banks are handled by the same driver, but in order to have a > working output on the bank B, we do need to set GPIO14 as soon as > we're probed. > > Just relying on the usual deferred probing introduces a circular > dependency between the gpio-regulator that needs to grab its GPIO from > a driver not there yet, and the gpio driver that needs to enable its > gpio-regulator. > > GPIO hogging needs to be the ideal solution for that, since we can > just enforce the GPIO14 value as the driver is probed, which provides > the guarantee that any driver using the bank B will actually drive the > GPIO it might use. > > However, an exclusive request will prevent any representation of this > as a regulator, which sounds a bit weird, since it really is just > that. Well that's elegant... I think it's a hog in this case though, not a GPIO regulator, definately not both. But let's check Mark's opinion on this. Yours, Linus Walleij -- 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
