> -----Original Message----- > From: Rafael J. Wysocki [mailto:r...@rjwysocki.net] > Sent: 2018年5月18日 15:55 > To: Peng Fan <peng....@nxp.com> > Cc: Rafael J. Wysocki <raf...@kernel.org>; Ulf Hansson > <ulf.hans...@linaro.org>; 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 Thursday, May 17, 2018 2:37:31 PM CEST Peng Fan wrote: > > > > > -----Original Message----- > > > From: rjwyso...@gmail.com [mailto:rjwyso...@gmail.com] On Behalf Of > > > Rafael J. Wysocki > > > Sent: 2018年5月17日 16:01 > > > To: Peng Fan <peng....@nxp.com> > > > Cc: Rafael J. Wysocki <raf...@kernel.org>; Ulf Hansson > > > <ulf.hans...@linaro.org>; 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 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. > > > > It is guest os not work well after guest os reboot. The hypervisor is not > affected. > > > > Thinking another case without hypervisor, M4 core run RTOS, A35 Core > > run Linux, when Linux rebooting, RTOS should not be affected. After > > Linux reboot itself, because its power domain is not paired with > open/shutdown, some devices not function well. > > The question boils down to whether or not devices should be detached from PM > domains on shutdown IMO. > > They are detached from PM domains on driver removal, so I guess one answer is > "yes, in analogy with that". However, the point about performace brought up > by Ulf seems to be valid too. > > In any case, the change should be made for all of the bus types using PM > domains, not just one.
Understand, it will increase shutdown time. How about shutdown the power domain in platform_driver->shutdown, let the driver handle it's power domain sthudown by itself? Then no need common framework change. Thanks, Peng