Re: [PATCH 7/7] ACPI / scan: Make memory hotplug driver use struct acpi_scan_handler

[Toshi Kani <toshi.kani@hp.com>]

On Wed, 2013-02-20 at 11:42 +0100, Vasilis Liaskovitis wrote:
> Hi Yasuaki,
> 
> On Wed, Feb 20, 2013 at 12:35:48PM +0900, Yasuaki Ishimatsu wrote:
> > Hi Vasilis,
> > 
> > 2013/02/20 3:11, Vasilis Liaskovitis wrote:
> > >Hi,
> > >
> > >On Sun, Feb 17, 2013 at 04:27:18PM +0100, Rafael J. Wysocki wrote:
> > >>From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > >>
> > >>Make the ACPI memory hotplug driver use struct acpi_scan_handler
> > >>for representing the object used to set up ACPI memory hotplug
> > >>functionality and to remove hotplug memory ranges and data
> > >>structures used by the driver before unregistering ACPI device
> > >>nodes representing memory.  Register the new struct acpi_scan_handler
> > >>object with the help of acpi_scan_add_handler_with_hotplug() to allow
> > >>user space to manipulate the attributes of the memory hotplug
> > >>profile.
> > >
> > >Let's consider an example where we want acpi memory device ejection to be safely
> > >handled by userspace. We do the following:
> > >
> > >echo 0 > /sys/firmware/acpi/hotplug/memory/autoeject
> > >echo 1 > /sys/firmware/acpi/hotplug/memory/uevents
> > >
> > >We succesfully hotplug acpi device:
> > >/sys/devices/LNXSYSTM:00/LNXSYSBUS:00/PNP0C80:00
> > >and its corresponding memblocks /sys/devices/system/memory/memoryXX are
> > >also successfully onlined.
> > >
> > >On an eject request, since uevents == 1, the kernel will emit KOBJ_OFFLINE for:
> > >/sys/devices/LNXSYSTM:00/LNXSYSBUS:00/PNP0C80:00
> > >
> > >Can userspace know which memblocks in /sys/devices/system/memory/memoryXX/
> > >correspond to the acpi device /sys/devices/LNXSYSTM:00/LNXSYSBUS:00/PNP0C80:00 ?
> > >This will be needed so that userspace tries to offline the memblocks (and only
> > >if successful, issue the eject operation on the acpi device). As far as I see,
> > >we don't create any sysfs links or files for this scenario - can userspace get
> > >this info somehow?
> > 
> > >
> > >/sys/devices/system/memory/memoryXX/phys_device needs to be properly implemented
> > >for this to work I think, see Documentation/ABI/testing/sysfs-memory
> > >
> > >The following test patch works toward that direction. Let me know if it's of
> > >interest or if there are better ideas /comments.
> > 
> > How about use ../PNP0C80:00/physical_node/resources file?
> > In my system, the file shows following information.
> > 
> > $ cat /sys/bus/acpi/devices/PNP0C80\:00/physical_node/resources
> > state = active
> > mem 0x0-0x80000000
> > mem 0x100000000-0x800000000
> > 
> > It means PNP0C80:00's memory ranges are "0x0-0x7fffffff" and
> > "0x100000000-0x7ffffffff". In x86 architecture, memory section size is
> > 128MiB. So, if these memory range is divided by 128MiB, you can
> > calculate memory section number as follow:
> > 
> > 0x0-0x7fffffff => 0x0-0x10
> > 0x100000000-0x7ffffffff => 0x20-0xff
> > 
> > But there is one problem. The problem is that resources file of added memory
> > is not created. If the problem is fixed, I think you can use the way.
> 
> thanks for your suggestion. Is this resources file a property of the
> physical_node or of each acpi devices? 
> 
> If it's a node specific file could there be a chance that adjacent memory
> ranges get merged? We 'd like these to not get merged.
> 
> I will look more into this property. I don't see it currently in my system
> (probably because initial memory is not backed by acpi devices in my
>  seabios/virtual machine).

I have been thinking about this issue as well.  In case of CPUs, we have
a sysdev link that links LNXCPU:%d to its system/cpu/cpu%d file.

/sys/bus/acpi/devices/LNXCPU:02 > ll sysdev
lrwxrwxrwx. 1 root root 0 Feb  8 13:52 sysdev -> ../../system/cpu/cpu2

So, one possible approach is to create a sysdev directory under
PNP0C080:%d, and then create links to associated system/cpu/memory%d
files underneath.  What do you think?

Thanks,
-Toshi