[RFC] the right way to use gpiolib hooks to automate power management?
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From: Gregory Bean on 12 Aug 2010 12:40 Hi folks: On MSM, we have a bank of gpios whose physical characteristics are controlled via a 'gpiomux' subsystem, which sets things like drive strength, pull-up, pull-down, gpio functional assignment, and the like. We have a written a software driver which reference-counts these gpio lines (via a put()/get() api), putting them in their "high-power" active configurations when they're in use, and dropping them down into a high-impedance low-power setting when they're not. We can't use gpiolib for this because many of these gpios are set to 'non-gpio' mux settings: they get assigned to busses as data or address lines (for example) and are not used as gpios after that. However, for those gpios which are left in 'gpio mode', we DO want gpiolib to 'do the right thing' as regards power management. From the following text in Documentation/gpio.txt: int gpio_request(unsigned gpio, const char *label); void gpio_free(unsigned gpio); ...Some platforms may also use knowledge about what GPIOs are active for power management, such as by powering down unused chip sectors and, more easily, gating off unused clocks... I interpret from this that it is 'healthy' behavior to put a call to our gpiomux get() in our gpio_chip's gpio_request(), and a matching call to our gpiomux put() in gpio_free(). It seems to me that this would bring lines out of low-power mode when they're first requested, and put them back to sleep when they're released, exactly as we want. Is this the right thing to be doing, or is this going to get us in trouble? I want to make sure we're using the system as it was intended. Thanks! -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |