Hi, On Thu, Dec 04, 2014 at 11:15:38PM +0900, Alexandre Courbot wrote: > On Wed, Dec 3, 2014 at 1:12 AM, 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. > > I don't get it. According to what you said, the following order should > go through IIUC: > > 1) bank A is probed, gpio 14 is available > 2) gpio-regulator is probed, acquires GPIO 14, regulator for Bank B is available > 3) bank B is probed, grabs its regulator and turn it on, probes. > > What am I missing? It would be true if bank A and B were exposed through different drivers (or at least different instances of the same driver), which is not the case. In our case, banks A and B are handled by the same instance. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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