| Message ID | 201106252329.24342.rjw@sisk.pl (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
"Rafael J. Wysocki" <rjw@sisk.pl> writes: > From: Rafael J. Wysocki <rjw@sisk.pl> > > Devices that are set up to wake up the system from sleep states > should not be stopped and power should not be removed from them > when the system goes into a sleep state. I don't think this belongs in the generic layer since the two assumptions above are not generally true on embedded systems, and would result in rather significant power consumption unnecessarily. First, whether the device should be stopped on device_may_wakeup(): Some IP blocks (at least on OMAP) have "asynchronous" wakeups. Meaning that they can generate wakeups even when they're not clocked (a.k.a stopped). So in this case, even after a ->stop_device (which clock gates the IP), it can still generate wakeups. Second, whether the device should be powered off if device_may_wakeup(): Embedded SoCs have other ways to wakeup than device-level wakeups. For example, on OMAP, every pad on the SoC can be configured as a wakeup source So, for example, you could completely power down the UART IP blocks (and the enclosing power domain), configure the UART RX pad as a wakeup source, and still wakeup the system on UART activity. The OMAP docs call these IO pad wakeups. On OMAP in fact, this is the common, default behavior when we enable "off-mode" in idle and/or suspend, since most of the IPs are powered off but can still wake up the system. So in summary, even if device_may_wakeup() is true, many devices (with additional SoC magic) can still generate wakeups even when stopped and powered off. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Index: linux-2.6/drivers/base/power/domain.c =================================================================== --- linux-2.6.orig/drivers/base/power/domain.c +++ linux-2.6/drivers/base/power/domain.c @@ -445,6 +445,9 @@ static int pm_genpd_suspend_noirq(struct if (ret) return ret; + if (device_may_wakeup(dev)) + return 0; + if (genpd->stop_device) genpd->stop_device(dev); @@ -665,6 +668,9 @@ static int pm_genpd_dev_poweroff_noirq(s if (ret) return ret; + if (device_may_wakeup(dev)) + return 0; + if (genpd->stop_device) genpd->stop_device(dev);