On Thu, 2014-10-02 at 01:21 +0200, Alexander Graf wrote: > > On 02.10.14 00:39, Scott Wood wrote: > > On Wed, 2014-10-01 at 15:27 +0200, Alexander Graf wrote: > >> The generic Linux framework to power off the machine is a function pointer > >> called pm_power_off. The trick about this pointer is that device drivers > >> can > >> potentially implement it rather than board files. > >> > >> Today on PowerPC we set pm_power_off to invoke our generic full machine > >> power > >> off logic which then calls ppc_md.power_off to invoke machine specific > >> power > >> off. > >> > >> However, when we want to add a power off GPIO via the "gpio-poweroff" > >> driver, > >> this card house falls apart. That driver only registers itself if > >> pm_power_off > >> is NULL to ensure it doesn't override board specific logic. However, since > >> we > >> always set pm_power_off to the generic power off logic (which will just not > >> power off the machine if no ppc_md.power_off call is implemented), we can't > >> implement power off via the generic GPIO power off driver. > >> > >> To fix this up, let's get rid of the ppc_md.power_off logic and just > >> always use > >> pm_power_off as was intended. Then individual drivers such as the GPIO > >> power off > >> driver can implement power off logic via that function pointer. > >> > >> With this patch set applied and a few patches on top of QEMU that > >> implement a > >> power off GPIO on the virt e500 machine, I can successfully turn off my > >> virtual > >> machine after halt. > > > > Are there any plans to handle restart similarly? > > I don't see an immediate need for it, as we do have access to reset via > the guts device.
The guts device is problematic from a hardware description perspective, as we advertise a bunch of things to the guest that we don't implement. E.g. the only reason we don't currently have a problem with Linux trying to use guts to sync the timebase across cores is that by chance we happen to expose a guts that corresponds to a single-cpu SoC. > I also don't see any generic driver in Linux that would implement reset > via a gpio controller device, so apparently it's not incredibly common > to implement reset via gpio. There wasn't a generic gpio-power-off driver either until a couple years ago... Regardless of whether it's done via gpio, using ppc_md for it is bad for the same reasons as for power-off. -Scott _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
