On Sun, Feb 03, 2013 at 05:28:09PM -0700, Toshi Kani wrote: > On Sat, 2013-02-02 at 16:01 +0100, Greg KH wrote: > > On Fri, Feb 01, 2013 at 01:40:10PM -0700, Toshi Kani wrote: > > > On Fri, 2013-02-01 at 07:30 +0000, Greg KH wrote: > > > > On Thu, Jan 31, 2013 at 06:32:18PM -0700, Toshi Kani wrote: > > > > > This is already done for PCI host bridges and platform devices and I don't > > > > > > see why we can't do that for the other types of devices too. > > > > > > > > > > > > The only missing piece I see is a way to handle the "eject" problem, i.e. > > > > > > when we try do eject a device at the top of a subtree and need to tear down > > > > > > the entire subtree below it, but if that's going to lead to a system crash, > > > > > > for example, we want to cancel the eject. It seems to me that we'll need some > > > > > > help from the driver core here. > > > > > > > > > > There are three different approaches suggested for system device > > > > > hot-plug: > > > > > A. Proceed within system device bus scan. > > > > > B. Proceed within ACPI bus scan. > > > > > C. Proceed with a sequence (as a mini-boot). > > > > > > > > > > Option A uses system devices as tokens, option B uses acpi devices as > > > > > tokens, and option C uses resource tables as tokens, for their handlers. > > > > > > > > > > Here is summary of key questions & answers so far. I hope this > > > > > clarifies why I am suggesting option 3. > > > > > > > > > > 1. What are the system devices? > > > > > System devices provide system-wide core computing resources, which are > > > > > essential to compose a computer system. System devices are not > > > > > connected to any particular standard buses. > > > > > > > > Not a problem, lots of devices are not connected to any "particular > > > > standard busses". All this means is that system devices are connected > > > > to the "system" bus, nothing more. > > > > > > Can you give me a few examples of other devices that support hotplug and > > > are not connected to any particular buses? I will investigate them to > > > see how they are managed to support hotplug. > > > > Any device that is attached to any bus in the driver model can be > > hotunplugged from userspace by telling it to be "unbound" from the > > driver controlling it. Try it for any platform device in your system to > > see how it happens. > > The unbind operation, as I understand from you, is to detach a driver > from a device. Yes, unbinding can be done for any devices. It is > however different from hot-plug operation, which unplugs a device. Physically, yes, but to the driver involved, and the driver core, there is no difference. That was one of the primary goals of the driver core creation so many years ago. > Today, the unbind operation to an ACPI cpu/memory devices causes > hot-unplug (offline) operation to them, which is one of the major issues > for us since unbind cannot fail. This patchset addresses this issue by > making the unbind operation of ACPI cpu/memory devices to do the > unbinding only. ACPI drivers no longer control cpu and memory as they > are supposed to be controlled by their drivers, cpu and memory modules. I think that's the problem right there, solve that, please. > > > > > 2. Why are the system devices special? > > > > > The system devices are initialized during early boot-time, by multiple > > > > > subsystems, from the boot-up sequence, in pre-defined order. They > > > > > provide low-level services to enable other subsystems to come up. > > > > > > > > Sorry, no, that doesn't mean they are special, nothing here is unique > > > > for the point of view of the driver model from any other device or bus. > > > > > > I think system devices are unique in a sense that they are initialized > > > before drivers run. > > > > No, most all devices are "initialized" before a driver runs on it, USB > > is one such example, PCI another, and I'm pretty sure that there are > > others. > > USB devices can be initialized after the USB bus driver is initialized. > Similarly, PCI devices can be initialized after the PCI bus driver is > initialized. However, CPU and memory are initialized without any > dependency to their bus driver since there is no such thing. You can create such a thing if you want :) > In addition, CPU and memory have two drivers -- their actual > drivers/subsystems and their ACPI drivers. Again, I feel that is the root of the problem. Rafael seems to be working on solving this, which I think is essencial to your work as well. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
