Re: [Qemu-devel] [PATCH 0/4] add ACPI Embedded Controller

[Michael S. Tsirkin]

On Tue, May 28, 2013 at 08:21:24AM +0800, li guang wrote:
> 在 2013-05-27一的 23:23 +0300，Michael S. Tsirkin写道：
> > On Mon, May 27, 2013 at 09:22:59AM +0800, li guang wrote:
> > > 在 2013-05-26日的 19:51 -0500，Anthony Liguori写道：
> > > > li guang <address@hidden> writes:
> > > > 
> > > > > 在 2013-05-24五的 14:45 +0300，Michael S. Tsirkin写道：
> > > > >> On Wed, May 22, 2013 at 11:46:33AM +0800, liguang wrote:
> > > > >> > These patches try to add ACPI Embedded Controller (EC),
> > > > >> > refer-to:
> > > > >> > ACPI SPEC v5 chapter 5 
> > > > >> > "ACPI Embedded Controller Interface Specification"
> > > > >> > 
> > > > >> > EC is a standard ACPI device, it plays flexible roles,
> > > > >> > e.g. 
> > > > >> > power controller, it can control power sequence for
> > > > >> > platform to enter or leave system state(0,1,3,4,5),
> > > > >> > it can controller CPU fan by the temperature of sensor.
> > > > >> > event carrier, it can pass events between platform
> > > > >> > and OS, so OS can execute _Qxx method which defined
> > > > >> > by yourself.
> > > > >> > 
> > > > >> > So, I want to deliver CPU online/offline event between
> > > > >> > OS and QEMU for CPU hotplug feature, then we will don't
> > > > >> > need to "echo 1 > /sys/devices/system/cpu/cpu1/online"
> > > > >> > again after 'cpu-add'.
> > > > >> > 
> > > > >> > patches for online/offline event handler of QEUM and 
> > > > >> > linux kernel are writing, and will send once finished.
> > > > >> > 
> > > > >> > since EC is a common device, so I send pathes separately.
> > > > >> 
> > > > >> Do any non-linux guests support this device?
> > > > >> 
> > > > >
> > > > > In fact, any OSes support ACPI will support this device.
> > > > > so, windows will.
> > > > 
> > > > When you say "any OSes supporting ACPI" I think what you really mean is
> > > > that we can provide bytecode that interacts with the embedded
> > > > controller.
> > > > 
> > > > There is not explicit driver in Linux or Windows AFAIK.
> > > 
> > > Hmm, yep, mostly there's no special driver for EC,
> > > because it is directly embedded in code for ACPI
> > > for linux kernel, it's drivers/acpi/ec.c
> > > 
> > > > 
> > > > I still don't get the point of this.  We can make ACPI hotplug work
> > > > without introducing a new device like this.
> > > > 
> > > 
> > > when you 'cpu-add' a cpu, acpi driver for cpu will not
> > > trigger 'cpu_up' for linux kernel AFAIK, unless you add
> > > a user space program to listen it's uevent and tigger 'cpu_up'.
> > > 
> > > and EC is not only for ACPI hotplug
> > > for example, the 'pvpanic', if there's a EC,
> > > we can pass pvpanic event by EC's ACPI space or Q-event,
> > > then we will not need this kind of special devices anymore.
> > > 
> > > 
> > 
> > 
> > So just to clarify: this patchset doesn't do anything useful
> > itself, 
> 
> the first patch is pure EC implementation which is useful.

Sorry, I didn't mean to imply that this is not useful,
merely that it is not yet directly useful for users.

> > it's some infrastructure that you want to build on
> > top of?
> 
> Yes, I'd like to use EC as infrastructure for my further development.
> 

I (and apparently others in this thread) would like to know some more
about planned use for this code before deciding on inclusion.

-- 
MST