On Mon, Aug 8, 2022 at 4:57 PM Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote: > On Sun, Aug 7, 2022 at 4:57 PM Ian Pilcher <arequipeno@xxxxxxxxx> wrote: > > > > I am trying to figure out how to use gpiod_get(), or one of its > > variants, to get the descriptor (struct gpio_desc *) for a specific > > GPIO. Getting a reference to the GPIO chip (struct gpio_chip *) is > > straightforward, and it provides a pointer to the device (.parent), but > > I absolutely cannot figure out what I am supposed to pass as the > > *con_id* argument. > > Ah, looking into your driver code [1] I think you need to a) switch to > use existing GPIO driver, which is gpio-ich.c in your case and b) use > GPIO lookup tables, you may look at Simatech latest development on how > to achieve that. It uses some Intel chips and LEDs that are connected > to GPIOs. Same for your I2C GPIO expander, why do you not use the kernel driver for it?! > > I know the offset of the GPIO on the chip, but I can't figure out how to > > use that. > > And you don't need to use GPIO offset, whatever it means. What you > need is to have a relative number of GPIO to the chip, so GPIO chip + > relative offset will uniquely give you the line. > > > Ultimately, my goal is to set the direction of the GPIO from within a > > "board setup" module. > > > > > > BACKGROUND > > > > I maintain an out-of-tree "board" module[1] that sets up the GPIOs and > > LEDs on my Thecus NAS. I am in the process of upgrading the OS on the > > NAS, which will require me to change the user-space daemon from the old > > sysfs GPIO interface to the new (non-ancient?) gpiod interface. > > > > One significant difference between the sysfs and gpiod interfaces, is > > that the new interface does not seem to provide an easy way to set a > > GPIO's direction (input/output) from a shell script[2]. Thus, I would > > like the board module to do that, along with the other setup. > > > > [1] https://github.com/ipilcher/n5550/blob/master/modules/n5550_board.c > > Why not try to upstream this? With the above additional remark I think you will learn a lot about Linux kernel programming if you try to upstream, even unsuccessfully (which I don't believe can happen if you listen to maintainers, e.g. PDx86 subsystem maintainer where your code belongs to). -- With Best Regards, Andy Shevchenko _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
