Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755629AbYLJPmi (ORCPT ); Wed, 10 Dec 2008 10:42:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753913AbYLJPmO (ORCPT ); Wed, 10 Dec 2008 10:42:14 -0500 Received: from az33egw02.freescale.net ([192.88.158.103]:58449 "EHLO az33egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753803AbYLJPmN (ORCPT ); Wed, 10 Dec 2008 10:42:13 -0500 From: Trent Piepho To: linux-kernel@vger.kernel.org Cc: Anton Vorontsov , linuxppc-dev@ozlabs.org, Richard Purdie , Trent Piepho , Grant Likely Subject: [PATCH 2/4] leds: Add option to have GPIO LEDs start on Date: Wed, 10 Dec 2008 07:41:41 -0800 Message-Id: <1228923703-16370-2-git-send-email-tpiepho@freescale.com> X-Mailer: git-send-email 1.5.4.1 In-Reply-To: <1228923703-16370-1-git-send-email-tpiepho@freescale.com> References: <1228923703-16370-1-git-send-email-tpiepho@freescale.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4871 Lines: 119 Yes, there is the "default-on" trigger but there are problems with that. For one, it's a inefficient way to do it and requires led trigger support to be compiled in. But the real reason is that is produces a glitch on the LED. The GPIO is allocate with the LED *off*, then *later* when then trigger runs it is turned back on. If the LED was already on via the GPIO's reset default or action of the firmware, this produces a glitch where the LED goes from on to off to on. While normally this is fast enough that it wouldn't be noticeable to a human observer, there are still serious problems. One is that there may be something else on the GPIO line, like a hardware alarm or watchdog, that is fast enough to notice the glitch. Another is that the kernel may panic before the LED is turned back on, thus hanging with the LED in the wrong state. This is not just speculation, but actually happened to me with an embedded system that has an LED which should turn off when the kernel finishes booting, which was left in the incorrect state due to a bug in the OF LED binding code. The platform device binding gains a field in the platform data "default_state" that controls this. The OpenFirmware binding uses a property named "default-state" that can be set to "on" or "off". The default if the property isn't present is off. Signed-off-by: Trent Piepho Acked-by: Grant Likely --- Documentation/powerpc/dts-bindings/gpio/led.txt | 9 ++++++++- drivers/leds/leds-gpio.c | 8 ++++++-- include/linux/leds.h | 1 + 3 files changed, 15 insertions(+), 3 deletions(-) diff --git a/Documentation/powerpc/dts-bindings/gpio/led.txt b/Documentation/powerpc/dts-bindings/gpio/led.txt index 4fe14de..5df384d 100644 --- a/Documentation/powerpc/dts-bindings/gpio/led.txt +++ b/Documentation/powerpc/dts-bindings/gpio/led.txt @@ -16,10 +16,15 @@ LED sub-node properties: string defining the trigger assigned to the LED. Current triggers are: "backlight" - LED will act as a back-light, controlled by the framebuffer system - "default-on" - LED will turn on + "default-on" - LED will turn on, but see "default-state" below "heartbeat" - LED "double" flashes at a load average based rate "ide-disk" - LED indicates disk activity "timer" - LED flashes at a fixed, configurable rate +- default-state: (optional) The initial state of the LED. Valid + values are "on" and "off". If the LED is already on or off and the + default-state property is set the to same value, then no glitch + should be produced where the LED momentarily turns off (or on). + The default is off if this property is not present. Examples: @@ -36,8 +41,10 @@ run-control { compatible = "gpio-leds"; red { gpios = <&mpc8572 6 0>; + default-state = "off"; }; green { gpios = <&mpc8572 7 0>; + default-state = "on"; }; } diff --git a/drivers/leds/leds-gpio.c b/drivers/leds/leds-gpio.c index 107b958..21084a3 100644 --- a/drivers/leds/leds-gpio.c +++ b/drivers/leds/leds-gpio.c @@ -92,9 +92,10 @@ static int __devinit create_gpio_led(const struct gpio_led *template, led_dat->cdev.blink_set = gpio_blink_set; } led_dat->cdev.brightness_set = gpio_led_set; - led_dat->cdev.brightness = LED_OFF; + led_dat->cdev.brightness = template->default_state ? LED_FULL : LED_OFF; - gpio_direction_output(led_dat->gpio, led_dat->active_low); + gpio_direction_output(led_dat->gpio, + led_dat->active_low ^ template->default_state); INIT_WORK(&led_dat->work, gpio_led_work); @@ -256,12 +257,15 @@ static int __devinit of_gpio_leds_probe(struct of_device *ofdev, memset(&led, 0, sizeof(led)); for_each_child_of_node(np, child) { unsigned int flags; + const char *state; led.gpio = of_get_gpio_flags(child, 0, &flags); led.active_low = flags & OF_GPIO_ACTIVE_LOW; led.name = of_get_property(child, "label", NULL) ? : child->name; led.default_trigger = of_get_property(child, "linux,default-trigger", NULL); + state = of_get_property(child, "default-state", NULL); + led.default_state = state && !strcmp(state, "on"); ret = create_gpio_led(&led, &pdata->led_data[pdata->num_leds++], &ofdev->dev, NULL); diff --git a/include/linux/leds.h b/include/linux/leds.h index d3a73f5..caa3987 100644 --- a/include/linux/leds.h +++ b/include/linux/leds.h @@ -138,6 +138,7 @@ struct gpio_led { const char *default_trigger; unsigned gpio; u8 active_low; + u8 default_state; }; struct gpio_led_platform_data { -- 1.5.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/