Messages in this thread | | | From | Christian Lamparter <> | Subject | Re: [PATCH v2] gpiolib: add hogs support for machine code | Date | Thu, 12 Apr 2018 22:00:07 +0200 |
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On Dienstag, 10. April 2018 22:30:28 CEST Bartosz Golaszewski wrote: > Board files constitute a significant part of the users of the legacy > GPIO framework. In many cases they only export a line and set its > desired value. We could use GPIO hogs for that like we do for DT and > ACPI but there's no support for that in machine code. > > This patch proposes to extend the machine.h API with support for > registering hog tables in board files. > > Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl> > --- > @@ -1326,6 +1364,8 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, > > acpi_gpiochip_add(chip); > > + machine_gpiochip_add(chip); > + > /* > * By first adding the chardev, and then adding the device, > * we get a device node entry in sysfs under > @@ -3462,6 +3502,33 @@ void gpiod_remove_lookup_table(struct gpiod_lookup_table *table)
I think I see the same problem right here in regards to pinctrls and gpiohogs that have with DeviceTree: <https://patchwork.kernel.org/patch/10313767/>
The problem is that unlike native gpio-controllers, pinctrls need to have a "pin/gpio range" defined before any gpio-hogs can be added.
If this is not the case the generic pinctrl_gpio_reguest() [0] will fail with -EPROBE_DEFER at this point. (see the call chain in the "pinctrl: msm: fix gpio-hog related boot issueslogin register" mail starting from gpiod_hog).
And now the crux of the matter is that currently in order for pinctrl drivers to register the range they have to call gpiochip_add_pin_range() [1]. But they only can do it after the gpiochip_add_data_with_key() [2], since this function initializes the pin_ranges list [3].
So what will happen is that you'll get an "gpiochip_machine_hog: unable to hog GPIO line $LABEL $GPIONR -517" error for every single gpio-hog and wonder why :(.
Regards, Christian
[0] <https://elixir.bootlin.com/linux/v4.16.2/source/drivers/pinctrl/core.c#L743> [1] <https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib.c#L2078> [2] <https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib.c#L1136> [3] <https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib.c#L1253>
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