On Friday 25 June 2021 01:18:43 Linus Walleij wrote: > On Wed, Jun 23, 2021 at 12:23 AM Pali Rohár <pali@xxxxxxxxxx> wrote: > > > Lorenzo asked a good question how GPIO drives PERST#. And maybe it would > > be a good idea to unify all pci controller drivers to use same GPIO > > value for asserting PERST# pin. If it is possible. As we can see it is a > > big mess. > > > > Personally I would like to a see two helper functions like > > > > void pcie_assert_perst(struct gpio_desc *gpio); > > void pcie_deassert_perst(struct gpio_desc *gpio); > > > > which pci controller driver will use and we will not more handle active > > high / low state or polarity inversion and meditate if gpio set to zero > > means assert or de-assert. > > GPIO descriptors (as are used in this driver) are supposed to hide > and encapsulate polarity inversion so: > > 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. > Whether the line is asserted by physically driving the line low or > high should not be a concern, that is handled in the machine > description, we support OF, ACPI and even board files to > define this. > > I would use gpiod_set_value() directly as above and maybe > add some comments explaining what is going on and that > the resulting polarity inversion is handled inside gpiolib. > > Because of common misunderstandings we have pondered to just > search/replace the last argument of gpiod_set_value() from > an (int value) to a (bool asserted) to make things clear. > I just never get around to do that. 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. > > Yours, > Linus Walleij
