Hi, On 25/06/21 02:09, Linus Walleij wrote: > On Fri, Jun 25, 2021 at 1:34 AM Pali Rohár <pali@xxxxxxxxxx> wrote: > >>> gpiod_set_value(gpiod, 1) == assert the line >>> gpiod_set_value(gpiod, 0) == de-assert the line >> >> Problem is that some pci controller drivers (e.g. pci-j721e.c or >> pcie-rockchip-host.c) expects that gpiod_set_value_cansleep(gpiod, 1) >> de-asserts the line and it is already used in this way. >> >> Which is opposite of the behavior which you wrote above. > > I sketched a way out of the problem using a quirk in > gpiolib in another response. We have a few of these > cases where we have to code our way out of mistakes, > such things happen. > > The problem is common, and due to the fact that device tree > authors ignores the flag GPIO_ACTIVE_HIGH (which has > been around since the early days of device tree on PowerPC) > instead they opt to do the inversion in code. Which violates the > contract that the DT should describe the hardware. > > The ambition of the DT specifications/schemas are to be operating > system independent, and this kind of stuff creates a situation > where other operating systems can't use the specification without > also going and looking at how Linux has implemented stuff. > Which is against the ambition of the device tree work. > >> I would suggest to define enum/macro with word ASSERT and DEASSERT in >> its name instead of just true/false boolean or 0/1 int. >> >> In case of this PERST# misunderstanding, having assert/deassert in name >> should really help. > > Hm that looks useful, Bart &co what do you think? > > #define GPIOD_ASSERTED 1 > #define GPIOD_DEASSERTED 0 > > in consumer.h, would that be helpful for users? Looks like a good idea to me. It would help making people aware that gpiod_set_value() & co do _not_ take a physical line value. It's done that way since ages, it's documented, yet many developers are still unaware of that... -- Luca
