Messages in this thread | | | From | Laurent Pinchart <> | Subject | Re: [PATCH] pinctrl: document the "GPIO mode" pitfall | Date | Fri, 26 Apr 2013 01:15:09 +0200 |
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Hi Linus,
On Thursday 25 April 2013 23:39:18 Linus Walleij wrote: > On Tue, Apr 23, 2013 at 3:33 PM, Laurent Pinchart wrote: > >> +And your machine configuration may look like this: > >> +-------------------------------------------------- > >> + > >> +static unsigned long uart_default_mode[] = { > >> + PIN_CONF_PACKED(PIN_CONFIG_DRIVE_PUSH_PULL, 0), > >> +}; > >> + > >> +static unsigned long uart_sleep_mode[] = { > >> + PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0), > >> +}; > > > > I'm having a bit of trouble with PIN_CONFIG_DRIVE_PUSH_PULL and > > PIN_CONFIG_OUTPUT. Strictly speaking, when configured in output mode, the > > pin will be in a push-pull configuration. > > For your system or for any system? Open drain, open source are also > output modes, and none of them are push-pull.
Indeed. I was actually thinking about the opposite, push-pull is output.
> > Could you clarify the exact scope of the two configuration parameters ? > > PIN_CONFIG_OUTPUT is left a bit unspecified, but here the idea was a passive > drive, like just connecting the pin to VDD or GND without any driver stage > at all.
Isn't that a driver stage ? :-)
> Maybe I should patch the documentation since we seem to be the only user? > > In the above case (which is derived from the ABx500) I think what is > happening is that the pin is connected to ground during sleep, without any > enabled driver stages, which saves a lot of power, since you do not need to > bias the totempole during sleep in that way.
Right. What is unclear to me is the interaction between OUTPUT and DRIVE_*. That's the part I would like to see clarified. Does DRIVE_* imply that the pin is driven by the selected function, and OUTPUT imply that the pin is driven to a fixed level ? If so, how do you configure the drive type of a pin that will be used through the GPIO API ? What about cases where I want to drive the pin to a fixed level in a non low-power output mode (for instance because I need more current that what the low-power output mode provides) ?
-- Regards,
Laurent Pinchart
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