On Mon, 2023-12-04 at 00:03 +0100, Linus Walleij wrote: > On Fri, Dec 1, 2023 at 4:24 PM Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > > > > If a pins .direction_output() fails, .set_value() will not be called > > > on it either. > > > > This is where I lost you :( > > devm_gpiod_get() (and similar interfaces) will set up the default mode for > the line, as input or output (with value, calling .direction_output) so most > likely it will fail already there, and the driver will not probe or > userspace client > will fail. > > > So, I'm might be overcomplicating things but... Again, > > the case where someone wired up HW so that we can actually use the pin to drive > > the > > line high (having an external pull up). In that case, If I return error, then I > > won't > > be able to effectively set the line high (as you said, set_value will not be > > called > > on it either). > > > > Now, I do understand that if we have the line flagged as GPIO_OPEN_DRAIN, then > > gpiolib will switch the line to input which means we will set the line in high-z > > which means that if we have a pull up, then the line will be high. I mean, it > > works > > but it would be strange if someone wants to have the line as output high and > > after > > trying to set the it high, it sees the pin moving to input. But if this is how it > > should be, fine by me. > > What do you mean by "sees the pin moving to input". > > If you mean electrically then yes, it goes to high-Z. > Ohh, I know where my failure was!! I was reading gpiod_direction_output(desc, 1) and following it only till gpiod_direction_input(desc). I was completely missing the 'set_output_flag' jump... All understood now :) > If you mean logically, as seen by software and GPIO and debugfs, not > really. > > I think a good exercise to see how it works is to just walk through the > code in drivers/gpio/gpiolib.c for e.g. > gpiod_set_value() > gpiod_set_value_nocheck() > gpio_set_open_drain_value_commit() > Hmm, by looking into those, it made me think that I should not even need to implement the .set() callback... > Thanks for all your help! - Nuno Sá
