From mboxrd@z Thu Jan 1 00:00:00 1970 From: hanjun.guo@linaro.org (Hanjun Guo) Date: Thu, 30 Apr 2015 21:38:32 +0800 Subject: [Discussion] how to implement external power down for ARM In-Reply-To: <20150430092953.GA32190@leverpostej> References: <55417F5A.4040300@linaro.org> <3341308.O9mDCt0NEl@wuerfel> <20150430092953.GA32190@leverpostej> Message-ID: <55423058.8010509@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2015?04?30? 17:29, Mark Rutland wrote: > On Thu, Apr 30, 2015 at 10:08:05AM +0100, Peter Maydell wrote: >> On 30 April 2015 at 09:03, Arnd Bergmann wrote: >>> On Thursday 30 April 2015 09:03:22 Shannon Zhao wrote: >>>> >>>> I am looking at adding support for external power down and reboot to >>>> ARM VMs. With ACPI this is fairly straight forward and requires only >>>> adding a GPIO controller to the virt machine model and extending ACPI >>>> appropriately (see code here [1]). In addition Linaro LEG also have >>>> done a test that uses GPIO as power button to shutdown OS on fast model >>>> (see detail here [2]). >>>> >>>> However, we would like for this to work in systems that do not use >>>> ACPI as well. Adding a GPIO controller will still work, but we would >>>> need a generic way to tell Linux how to handle the GPIO events without >>>> adding any board-specific code to the VIRT platform. And what guest >>>> kernel driver do we need? Do we need another user-level daemon like acpid? >>>> >>>> Note that external shutdown can also be accomplished using the qemu >>>> guest agent [3], but maybe this is not a sufficiently stable approach. >>>> >>>> Any input on the approach to take here is very welcome. >>> >>> I would expect drivers/power/reset/gpio-poweroff.c to work in an identical >>> way with ACPI and DT, once you have added an ACPI binding for it. >> >> Looking at Documentation/devicetree/bindings/gpio/gpio-poweroff.txt >> that appears to be for "let the guest kernel turn off the system >> from the inside by toggling a GPIO line". What we want is the >> opposite: the external system (QEMU, in this case) toggles a GPIO >> line in order to request the guest kernel to do a clean shutdown >> or reboot. Or have I misunderstood what gpio-poweroff can do? > > No, you're correct. > > There are a few "power button" bindings around, but it looks like they > all rely on platform details and aren't that generic. > > With ACPI what events may be singalled? Just power off, or reset, etc? For the ACPI events, we generally have three events: - sleep event - power off event - wakeup event > > Which of these do we need to be able to handle with DT? I think power off event is the most used event, sleep and wakeup events are often used for laptops. For ACPI based power off, there will be a GPIO singled event (hardware reduced platform such as ARM64) or a special interrupt called SCI signaled to OS to let OS know there is a button event happened, then there is a driver handle this interrupt to tell the detail event, the driver will send the event to user space using input framework(deprecated) or netlink event. I think DT can do it in a similar way, using input framework or netlink sending power button to user space and shutdown the system. If any detail information needed, please let me know. Thanks Hanjun