On Thu, Dec 04, 2014 at 11:49:19PM +0900, Alexandre Courbot wrote: > On Thu, Dec 4, 2014 at 11:27 PM, Maxime Ripard > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > > 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. > > Ok, so both banks A and B are part of the same device/DT node. Now I > think I understand the issue. You need to hog the pin so that bank B > will work right after the device is probed. Exactly. > But you will still have the problem that the regulator device will > *not* be available when your device is probed, so you cannot call > regulator_get() for bank B anyway. I guess your only choice is to hog > that pin and leave it active ad vitam eternam. Hmmm, indeed. I'll stop boring you with this then :) Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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