On Thu, May 17, 2018 at 4:33 AM, Peng Fan <peng....@nxp.com> wrote: > > >> -----Original Message----- >> From: rjwyso...@gmail.com [mailto:rjwyso...@gmail.com] On Behalf Of Rafael >> J. Wysocki >> Sent: 2018年5月17日 5:35 >> To: Ulf Hansson <ulf.hans...@linaro.org> >> Cc: Peng Fan <peng....@nxp.com>; Rafael J. Wysocki >> <rafael.j.wyso...@intel.com>; Fabio Estevam <fabio.este...@nxp.com>; Greg >> Kroah-Hartman <gre...@linuxfoundation.org>; Linux Kernel Mailing List >> <linux-kernel@vger.kernel.org>; Linux PM <linux...@vger.kernel.org>; >> dl-linux-imx <linux-...@nxp.com> >> Subject: Re: [RFC] platform: detach from PM domains on shutdown >> >> On Wed, May 16, 2018 at 11:52 AM, Ulf Hansson <ulf.hans...@linaro.org> >> wrote: >> > On 15 May 2018 at 11:01, Peng Fan <peng....@nxp.com> wrote: >> >> When reboot Linux, the PM domains attached to a device are not >> >> shutdown. To SoCs which relys on reset the whole SoC, there is no >> >> need to shutdown PM domains, but to Linux running in a virtual >> >> machine with devices pass-through, we could not reset the whole SoC. >> >> Currently we need Linux to shutdown its PM domains when reboot. >> > >> > I am not sure I understand exactly why the PM domain needs to be >> > shutdown for these cases, could you please elaborate a bit on that. >> > >> > BTW, what platform are you running on and also what PM domains are being >> used? >> > >> > Anyway, it seems like there may be need for certain cases, but >> > certainly not all - especially since it may slow down the shutdown >> > process, when not needed. >> > >> > Can we make this runtime configurable, via sysfs or whatever that makes >> sense!? >> > >> >> >> >> commit 2d30bb0b3889 ("platform: Do not detach from PM domains on >> >> shutdown"), removes what this patch tries to add, because of a warning. >> >> commit e79aee49bcf9 ("PM: Avoid false-positive warnings in >> >> dev_pm_domain_set()") already fixes the false alarm warning. So let's >> >> detach the power domain to shutdown PM domains after driver shutdown. >> >> >> >> Signed-off-by: Peng Fan <peng....@nxp.com> >> >> --- >> >> >> >> I do not find a better place to shutdown power domain when reboot >> >> Linux, so add back the line that commit 2d30bb0b3889 removes, because >> >> it is a false alarm warning as commit e79aee49bcf9 describes. >> >> >> >> drivers/base/platform.c | 1 + >> >> 1 file changed, 1 insertion(+) >> >> >> >> diff --git a/drivers/base/platform.c b/drivers/base/platform.c index >> >> 8075ddc70a17..a5929f24dc3c 100644 >> >> --- a/drivers/base/platform.c >> >> +++ b/drivers/base/platform.c >> >> @@ -616,6 +616,7 @@ static void platform_drv_shutdown(struct device >> >> *_dev) >> >> >> >> if (drv->shutdown) >> >> drv->shutdown(dev); >> >> + dev_pm_domain_detach(_dev, true); >> > >> > This would somewhat work, but only for platform devices. To make this >> > fully work, we need to call dev_pm_domain_detach() from amba, spi, etc >> > as well. >> > >> > Perhaps another option to manage this more generally, an without >> > having detach devices, could be to extend the struct dev_pm_domain >> > with a new callback, "->shutdown()" and then make the driver core call >> > it from device_shutdown(). >> >> I'm sensing a possible ordering slippery slope with this (it will only work >> if all of >> the drivers/bus types etc do the right thing in their >> ->shutdown callbacks so nothing depends on the domain going forward). >> >> > Typically, for genpd, I would probably count the number of calls being >> > made to ->shutdown() per PM domain, then when it reaches the number of >> > attached devices to it, allow to power off it. >> > >> > Let's see what Rafael thinks about it. >> >> I'm not sure about the use case. The hypervisor should be able to take care >> of >> turning power domains off on the client OS reboot in theory. If the client >> OS >> leaving the hypervisor needs to worry about what state it leaves behind, the >> design of the hypervisor is sort of questionable IMO. > > This is valid concern. But moving the power domain logic into hypervisor > mostly micro-kernel design > will introduce more complexity and make certification harder. > Currently, Let Linux shutdown it's power domain is the easiest way to me and > make things work well > after reboot.
Well, to put it bluntly, if your hypervisor depends on the guest to do the right thing on exit, it doesn't do its job. I wouldn't have certified it for you if that was my decision.
