On Mon, Feb 20, 2012 at 8:39 AM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Sun, Feb 19, 2012 at 11:27:42PM -0700, Stephen Warren wrote: >> Update gpio.txt based on recent discussions regarding interaction with the >> pinctrl subsystem. >> >> Previously, gpio_request() was described as explicitly not performing any >> required mux setup operations etc. >> >> Now, gpio_request() is explicitly as explicitly performing any required mux >> setup operations where possible. In the case it isn't, platform code is >> required to have set up any required muxing or other configuration prior to >> gpio_request() being called, in order to maintain the same semantics. > > So what if you need to have the pin as a GPIO, manipulate it as a GPIO, > and then hand it off to a special function, and then take it back as > a GPIO before you shut the special function down ? I remember this case very well and we designed for it, so it should be handled by pin control and GPIO thusly: Example: use pins 1,2 as I2C, then convert them to GPIO for a while then back again: // This call looks up a map containing pins 1,2 and reserve them p = pinctrl_get(dev, "i2c"); if (IS_ERR(p)) ... pinctrl_enable(p); pinctrl_disable(p); // This will free up the pins again pinctrl_put(p); // So now we can do this... // NB: the GPIO driver calls pinctr_request_gpio() to check // that it can take these pins gpio_request(1, "gpio1"): gpio_request(2, "gpio2"); // This will trigger a reset or something gpio_direction_output(1, 1); gpio_direction_output(2, 1); // Release pins again gpio_free(1); gpio_free(2); // Take them back for this function p = pinctrl_get(dev, "i2c"); It's a bit kludgy but works and makes sure the pins are only used for one thing at a time. BTW: Russell, which specific platform and driver was it that had this usecase? I'd like to have a look at the code to educate myself. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
