On 30/11/15 22:42, Rafael J. Wysocki wrote: > On Monday, November 30, 2015 04:42:46 PM Jon Hunter wrote: >> Currently, if PM is disabled in the kernel then so is >> PM_GENERIC_DOMAINS. Although this makes sense, I can see a scenario >> where having minimal genpd support could be advantageous. >> >> I am looking at enabling genpd for Tegra and ideally we would populate >> the power domains when the platform device is probed for the power >> management controller (PMC) as this device contains the registers for >> enabling the power domains. >> >> This works fine for the case where PM is enabled, but I am concerned >> about the case where we don't have PM enabled in the kernel. In this >> case, because domains are not populated early during the boot process, I >> am concerned that there is a chance for a device dependent on a power >> domain to be probed before the PMC device has been probed and had chance >> to turn on any power domains. > > So make the !PM case invalid for that platform. Thierry, I know that we have not reviewed GPD for tegra recently, but what are your thoughts on the above in principle? At least for Tegra 64-bit? > Seriously, either PM is mandatory, or it isn't. If it is mandatory, make it so > instead of pretending that you can live without it. I understand your point and I do agree, however, this means that for any device with power-domains that PM is already mandatory (unless they don't use genpd at all). I see some platforms getting around this by enabling all the power-domains early during the platform code and if PM is not enabled then they won't be turned off and so all is ok (d438462c20a3 "ARM: imx6: gpc: always enable PU domain if CONFIG_PM is not set"). However, this assumes that power-domains will never fail to power on and this seems a little fragile to me. One thought I had was to make the PM_GENERIC_DOMAINS_OF code independent of PM (ie. moved to domain_of.c) and with a little tweaking of the genpd_dev_pm_attach() function it could be made to work whether PM is enable or not. In other words, if PM is not enabled, then genpd_dev_pm_attach() would only return success if: 1. The device is not dependent on a power domain or 2. The device is dependent on a power domain and it is present and already powered on. Alternatively, may be genpd_dev_pm_attach() should always return -EPROBE_DEFER (to prevent probing a device) if !PM and the device has a "power-domains" node defined. Cheers Jon -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
