Messages in this thread | | | From | Laurent Pinchart <> | Subject | Re: [PATCH] pinctrl: establish pull-up/pull-down terminology | Date | Sat, 22 Jun 2013 01:30:18 +0200 |
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Hi Stephen,
On Friday 21 June 2013 13:06:47 Stephen Warren wrote: > 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 <linus.walleij@linaro.org> > >>> > >>> 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 <heiko@sntech.de> > >>> Cc: James Hogan <james.hogan@imgtec.com> > >>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com> > >>> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> > >>> --- > >>> > >>> 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 may be mistaken, but I've understood the PULL_PIN_DEFAULT option as a way to select the default bias configuration when the default value is hardware- controlled, not as a pure software option.
> 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.
-- Regards,
Laurent Pinchart
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