From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from na01-bn1-obe.outbound.protection.outlook.com (mail-bn1bon0135.outbound.protection.outlook.com [157.56.111.135]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 2EE171A17FD for ; Thu, 2 Oct 2014 09:29:00 +1000 (EST) Message-ID: <1412206127.13320.362.camel@snotra.buserror.net> Subject: Re: [PATCH 00/20] powerpc: Convert power off logic to pm_power_off From: Scott Wood To: Alexander Graf Date: Wed, 1 Oct 2014 18:28:47 -0500 In-Reply-To: <542C8C69.2010509@suse.de> References: <1412170086-57971-1-git-send-email-agraf@suse.de> <1412203153.13320.352.camel@snotra.buserror.net> <542C8C69.2010509@suse.de> Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Cc: Arnd Bergmann , Geoff Levand , Alistair Popple , Anatolij Gustschin , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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