Hi Geert, On Tue, Jun 16, 2015 at 02:36:48PM +0200, Geert Uytterhoeven wrote: > If a GPIO driver uses gpiochip_add_pin_range() (which is usually the > case for GPIO/PFC combos), the GPIO hogging mechanism configured from DT > doesn't work: > > requesting hog GPIO lcd0 (chip r8a7740_pfc, offset 176) failed > > The actual error code is -517 == -EPROBE_DEFER. > > The problem is that PFC+GPIO registration is handled in multiple steps: > 1. pinctrl_register(), > 2. gpiochip_add(), > 3. gpiochip_add_pin_range(). > > Configuration of the hogs is handled in gpiochip_add(): > > gpiochip_add > of_gpiochip_add > of_gpiochip_scan_hogs > gpiod_hog > gpiochip_request_own_desc > __gpiod_request > chip->request > pinctrl_request_gpio > pinctrl_get_device_gpio_range > > However, at this point the GPIO controller hasn't been added to > pinctrldev_list yet, so the range can't be found, and the operation fails > with -EPROBE_DEFER. > > - Exchanging the order of the calls to gpiochip_add() and > gpiochip_add_pin_range() is not an option, as the latter depends on > initialization done by the former. > - Just moving the call of of_gpiochip_scan_hogs() from gpiochip_add() > to gpiochip_add_pin_range() is also not an option, as the latter is > optional, and thus not used by all drivers. > > Hence if of_gpiochip_scan_hogs() fails with -EPROBE_DEFER, call it > again every time the pin range is changed, until it succeeded. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > --- > Questions: > - Is there a better solution to handle this? > > - Should the pin ranges be configured by passing an array of data to > gpiochip_add() instead of having calls to gpiochip_add_pin_range()? > That would require changing all drivers. > > - What happens if you have multiple hogs in multiple ranges? > The first hog(s) may be configured multiple times. Is that a problem? > > - In one of the threads that discussed the GPIO hogging mechanism, Maxime > Ripard said: "Our pinctrl driver is also our GPIO driver, so they both > share the same node." > Maxime: Did you try GPIO hogging? Did it work? > If yes, which driver are you using? What's different compared to sh-pfc? > If no, did you get it to work? I'm using pinctrl-sunxi, and no, I haven't tried it yet, so it probably have the issue you reported :) Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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