[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug prop
Re: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug property for pcie-root-ports
Fri, 26 Nov 2021 11:12:55 +0530 (IST)
Alpine 2.22 (DEB 394 2020-01-19)
On Thu, 25 Nov 2021, Michael S. Tsirkin wrote:
> On Thu, Nov 25, 2021 at 05:36:29PM +0530, Ani Sinha wrote:
> > x-native-hotplug property, when used in order to disable HPC bit on the PCIE
> > root ports, can lead to unexpected results from the guest operating system.
> > Users are strongly advised not to touch this property in order to manipulte
> > the
> > HPC bit. Add a word of caution in the pcie.txt doc file to document this.
> > Signed-off-by: Ani Sinha <email@example.com>
> Do we want to generally document this for all "x-" options?
Yes igor suggested it but I sent this one for two reasons:
(a) I could not find a place to document this for properties without
adding a new file. This sounded too bigger a hammer at the present. If you
can suggest an existing place for documenting this for the property names,
I will go and add this info there as well.
(b) I think we need to document this experimental property here regardless
because this doc deals with hotplug and pcie ports and we had too much of
a mess with this acpi/pci native switch.
When things stabilize a bit, Igor suggested elsewhere that we start a
separate doc just for hotplug and various options we have and at
that point we can move this info in this new doc.
> > ---
> > docs/pcie.txt | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> > diff --git a/docs/pcie.txt b/docs/pcie.txt
> > index 89e3502075..e1f99f725f 100644
> > --- a/docs/pcie.txt
> > +++ b/docs/pcie.txt
> > @@ -262,11 +262,26 @@ PCI Express Root Ports (and PCI Express Downstream
> > Ports).
> > Port, which may come handy for hot-plugging another device.
> > -5.3 Hot-plug example:
> > +5.2 Hot-plug example:
> > Using HMP: (add -monitor stdio to QEMU command line)
> > device_add <dev>,id=<id>,bus=<PCI Express Root Port Id/PCI Express
> > Downstream Port Id/PCI-PCI Bridge Id/>
> > +5.3 A word of caution using hotplug on PCI Express Root Ports:
> > +Starting Qemu version 6.2, PCI Express Root ports have a property
> > +"x-native-hotplug" ("native-hotplug" for Qemu version 6.1), that can be
> > used to
> > +enable or disable hotplug on that port. For example:
> > +
> > +-device pcie-root-port,x-native-hotplug=off,... etc.
> > +
> > +The "x-" prefix indicates that this property is highly experimental and can
> > +lead to unexpected results from the guest operating system if users try to
> > use
> > +it to alter the native hotplug on the port. It also means that the property
> > +name and its behavior is liable to change in the future and is not
> > expected to
> > +be stable across Qemu versions. Therefore, end users are advised not to
> > change
> > +the value of this option from its default set value or use it in the Qemu
> > +command line.
> > +
> > 6. Device assignment
> > ====================
> > Host devices are mostly PCI Express and should be plugged only into
> > --
> > 2.25.1