On Tue, Aug 18, 2015 at 4:34 AM, Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxx> wrote: > On Sun 16 Aug 23:59 PDT 2015, Alexandre Courbot wrote: > >> On Thu, Aug 13, 2015 at 10:06 PM, Linus Walleij >> <linus.walleij@xxxxxxxxxx> wrote: >> > On Tue, Aug 11, 2015 at 12:41 AM, Bjorn Andersson >> > <bjorn.andersson@xxxxxxxxxxxxxx> wrote: >> > >> >> But then the question first goes to Linus & co. >> >> >> >> gpio_chip->get() can return a negative value to indicate errors (and did >> >> so in this case), all parts of the API seems indicates that we can get >> >> an error (int vs bool). >> > >> > Ooops. >> > >> >> Should we change _gpiod_get_raw_value() to propagate this error? >> > >> > Yes for now. Can you patch it? :) >> > >> >> Or >> >> should we just ignore this issue and propagate an error as GPIO high >> >> reading? >> > >> > I don't know about the future. In some sense GPIOs are so smallish >> > resources that errorhandling every call to read/write them seem to >> > be a royal PITA. That is why I wanted to switch them to bool and get >> > rid of the problem, but now I also see that maybe that was not such a >> > smart idea, if errors do occur on the set/get_value path. >> >> Nowadays GPIOs may reside at the other end of an i2c bus, which means >> that even the simplest operation like reading a GPIO value can >> potentially fail. And it will probably not get better - wait until we >> implement GPIO-over-IP! :) >> > > Now that's progress! I can't wait ;) > >> So I'd say it makes sense to propagate errors returned by the driver's >> get() hook. This might contradict some of our earlier statements about >> simplifying the GPIO API, but is preferrable to having to make a >> decision as to which valid value to return if the driver fails... >> > > Sounds good. > > As we're patching up _gpiod_get_raw_value(), is the lack of a get() > implementation the same as a LOW or is that -ENOTSUPP? I don't see any reason why it should not be -ENOTSUPP if we start to manage errors properly. > >> It should then be made very clear in the documentation that the only >> positive values ever returned by the GPIO API will be 0 and 1 (we >> already have a clamping mechanism for that IIRC), and that negative >> values are propagated as-is. >> > > That makes sense. I'm however not able to find such clamping > macro/mechanism and it would be very beneficial here... > >> Linus, does that seem reasonable to you? Does anyone has the intention >> to address that one or should I add it to my short-term TODO list? > > If you have some input on above (is lack of get() an error) I can hack > up the patch. Excellent - since Linus gave his thumb up, I think you can go ahead. Looking forward to seeing this finally fixed. Thanks! Alex. -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
