On Wednesday, January 30, 2013 07:57:45 PM Toshi Kani wrote:
> On Tue, 2013-01-29 at 23:58 -0500, Greg KH wrote:
> > On Thu, Jan 10, 2013 at 04:40:19PM -0700, Toshi Kani wrote:
> > > +/*
> > > + * Hot-plug device information
> > > + */
> >
> > Again, stop it with the "generic" hotplug term here, and everywhere
> > else. You are doing a very _specific_ type of hotplug devices, so spell
> > it out. We've worked hard to hotplug _everything_ in Linux, you are
> > going to confuse a lot of people with this type of terms.
>
> Agreed. I will clarify in all places.
>
> > > +union shp_dev_info {
> > > + struct shp_cpu {
> > > + u32 cpu_id;
> > > + } cpu;
> >
> > What is this? Why not point to the system device for the cpu?
>
> This info is used to on-line a new CPU and create its system/cpu device.
> In other word, a system/cpu device is created as a result of CPU
> hotplug.
>
> > > + struct shp_memory {
> > > + int node;
> > > + u64 start_addr;
> > > + u64 length;
> > > + } mem;
> >
> > Same here, why not point to the system device?
>
> Same as above.
>
> > > + struct shp_hostbridge {
> > > + } hb;
> > > +
> > > + struct shp_node {
> > > + } node;
> >
> > What happened here with these? Empty structures? Huh?
>
> They are place holders for now. PCI bridge hot-plug and node hot-plug
> are still very much work in progress, so I have not integrated them into
> this framework yet.
>
> > > +};
> > > +
> > > +struct shp_device {
> > > + struct list_head list;
> > > + struct device *device;
> >
> > No, make it a "real" device, embed the device into it.
>
> This device pointer is used to send KOBJ_ONLINE/OFFLINE event during CPU
> online/offline operation in order to maintain the current behavior. CPU
> online/offline operation only changes the state of CPU, so its
> system/cpu device continues to be present before and after an operation.
> (Whereas, CPU hot-add/delete operation creates or removes a system/cpu
> device.) So, this "*device" needs to be a pointer to reference an
> existing device that is to be on-lined/off-lined.
>
> > But, again, I'm going to ask why you aren't using the existing cpu /
> > memory / bridge / node devices that we have in the kernel. Please use
> > them, or give me a _really_ good reason why they will not work.
>
> We cannot use the existing system devices or ACPI devices here. During
> hot-plug, ACPI handler sets this shp_device info, so that cpu and memory
> handlers (drivers/cpu.c and mm/memory_hotplug.c) can obtain their target
> device information in a platform-neutral way. During hot-add, we first
> creates an ACPI device node (i.e. device under /sys/bus/acpi/devices),
> but platform-neutral modules cannot use them as they are ACPI-specific.
But suppose we're smart and have ACPI scan handlers that will create
"physical" device nodes for those devices during the ACPI namespace scan.
Then, the platform-neutral nodes will be able to bind to those "physical"
nodes. Moreover, it should be possible to get a hierarchy of device objects
this way that will reflect all of the dependencies we need to take into
account during hot-add and hot-remove operations. That may not be what we
have today, but I don't see any *fundamental* obstacles preventing us from
using this approach.
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.
Thanks,
Rafael
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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