On 06/20/2013 06:38 AM, James Hogan wrote: > On 19/06/13 23:03, Stephen Warren wrote: >> On 06/16/2013 04:45 AM, Linus Walleij wrote: >>> From: Linus Walleij <[email protected]> >>> >>> It is counter-intuitive to have "0" mean disable in a boolean >>> manner for electronic properties of pins such as pull-up and >>> pull-down. Therefore, define that a pull-up/pull-down argument >>> of 0 to such a generic option means that the pin is >>> short-circuited to VDD or GROUND. Pull disablement shall be >>> done using PIN_CONFIG_BIAS_DISABLE. >>> >>> Cc: Heiko St�bner <[email protected]> >>> Cc: James Hogan <[email protected]> >>> Cc: Laurent Pinchart <[email protected]> >>> Signed-off-by: Linus Walleij <[email protected]> >>> --- >>> include/linux/pinctrl/pinconf-generic.h | 13 +++++++------ >>> 1 file changed, 7 insertions(+), 6 deletions(-) >>> >>> diff --git a/include/linux/pinctrl/pinconf-generic.h >>> b/include/linux/pinctrl/pinconf-generic.h >>> index d414a77..67780f5 100644 >>> --- a/include/linux/pinctrl/pinconf-generic.h >>> +++ b/include/linux/pinctrl/pinconf-generic.h >>> @@ -36,14 +36,15 @@ >>> * tristate. The argument is ignored. >>> * @PIN_CONFIG_BIAS_PULL_UP: the pin will be pulled up (usually with high >>> * impedance to VDD). If the argument is != 0 pull-up is enabled, >>> - * if it is 0, pull-up is disabled. >>> + * if it is 0, pull-up it total, i.e. the pin is connected to VDD. >>> * @PIN_CONFIG_BIAS_PULL_DOWN: the pin will be pulled down (usually with >>> high >>> * impedance to GROUND). If the argument is != 0 pull-down is enabled, >>> - * if it is 0, pull-down is disabled. >>> + * if it is 0, pull-down is total, i.e. the pin is connected to GROUND. >>> * @PIN_CONFIG_BIAS_PULL_PIN_DEFAULT: the pin will be pulled up or down >>> based >>> * on embedded knowledge of the controller, like current mux function. >>> - * If the argument is != 0 pull up/down is enabled, if it is 0, >>> - * the pull is disabled. >>> + * If the argument is != 0 pull up/down is enabled, if it is 0, the >>> + * configuration is ignored. The proper way to disable it is to use >>> + * @PIN_CONFIG_BIAS_DISABLE. >> >> Why treat PULL_UP/PULL_DOWN differently from PULL_PIN_DEFAULT? >> PULL_PIN_DEFAULT is logically simply a macro that selects PULL_UP/DOWN >> based on what's "normal" for the pin's expected usage, so surely the >> value associated with that option should behave identically? > > I'm not familiar with hardware that does this so I could be way wrong > here, but presumably if there's a default up/down, there's probably a > default resistance too. Does it really make sense to say > "pull up or down depending on whatever the pin is intended for... but > whichever it is must be XXX Ohm"? > If you know the resistance you want, you surely already know whether you > want it pull up or down with that resistence.
IIRC the idea of the PULL_PIN_DEFAULT was to avoid having to specify UP/DOWN for each pin/group, but could just say "default", which would then reduce the number of pinctrl mapping table entries or pinctrl DT property entries. I don't think this would have any interaction with setting the resistance; it's entirely plausible that you'd want the same explicit, or same default, resistance, for all pins, irrespective of pull-up vs. down. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
