On Sat, 02 Dec 2023 09:36:47 +0100 Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > On Fri, 2023-12-01 at 11:01 -0600, David Lechner wrote: > > On Fri, Dec 1, 2023 at 2:47 AM Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > > > > > > On Thu, 2023-11-30 at 15:41 -0600, David Lechner wrote: > > > > On Tue, Nov 21, 2023 at 4:17 AM Nuno Sa via B4 Relay > > > > <devnull+nuno.sa.analog.com@xxxxxxxxxx> wrote: > > > > > > > > > > From: Nuno Sa <nuno.sa@xxxxxxxxxx> > > > > > > > > > > The reset gpio was being requested with GPIOD_OUT_LOW which means, not > > > > > asserted. Then it was being asserted but never de-asserted which means > > > > > the devices was left in reset. Fix it by de-asserting the gpio. > > > > > > > > It could be helpful to update the devicetree bindings to state the > > > > expected active-high or active-low setting for this gpio so it is > > > > clear which state means asserted. > > > > > > > > > > You could state that the chip is active low but I don't see that change that > > > important for now. Not sure if this is clear and maybe that's why your comment. > > > GPIOD_OUT_HIGH has nothing to do with active high or low. It just means, "get me > > > the > > > pin in the asserted state". > > > > > > > I would assume that this bug happened in the first place because > > someone forgot GPIOD_OUT_LOW in the devicetree when they were > > developing the driver. So this is why I suggested that updating the > > devicetree binding docs so that future users are less likely to make > > the same mistake. Currently, the bindings don't even have reset-gpios > > in the examples. > > Hmm, I think you're missing the point... The bug has nothing to do with devicetree. > This is what was happening: > > 1) We were calling devm_gpiod_get_optional() with GPIOD_OUT_LOW. What this means is > that you get an output gpio deasserted. Hence the device is out of reset. And here is > the important part... what you have in dts does not matter. If you have active low, > it means the pin level will be 1. If you have high, the pin level is 0. And this is > all handled by gpiolib for you. > > 2) Then, we called gpiod_direction_output(..., 1), which means set the direction out > (which is actually not needed since it was already done when getting the pin) and > assert the pin. Hence, reset the device. And we were never de-asserting the pin so > the device would be left in reset. Functionally I believe David is correct. Flipping the DT would 'fix' this. It's all down to a nreset vs reset pin description. In this case I guess it's defined a a 'not reset' on the datasheet which is what is causing the confusion. It's not uncommon for people to refer to a reset when they mean a "not reset" with assumptions on polarity to match. Jonathan > > - Nuno Sá
