Re: [PATCH 2/2] qapi: introduce DEVICE_POWER_ON for SHPC hotplug

[Vladimir Sementsov-Ogievskiy]

On 11/16/22 19:26, Michael S. Tsirkin wrote:
> On Wed, Nov 16, 2022 at 07:12:34PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > Hi all! That's an RFC patch.
> >
> > The problem is that SHPC protocol says that power-led is blinking for 5
> > seconds before actual turning-on the device. If we call device-del
> > during this time the attention button press is ignored and we never get
> > DEVICE_DELETED event, which is unexpected for the user.
> >
> > I suggest add a pair for DEVICE_DELETED: DEVICE_POWER_ON. So user
> > should wait for DEVICE_POWER_ON after device-add before making any
> > other operations with the device (incluing device-del).
> >
> > What I'm unsure is what about other types of hotplug - PCIE and
> > ACPI.. Do they suffer from similar problems?
> I didn't yet look at this patchset deeply (we are in freeze anyway)
> but PCIE is substancially same as SHPC.
>
> Take a look at Gerd's "improve native hotplug for pcie root ports"
> same kind of approach probably works for SHPC.

Looking at it. Yes, I think this approach is OK, thanks for the link.

I doubt now that we really need new event. Instead I can update SHPC to return an error 
when trying to unplug with blinking power indicator (like 81124b3c7a5dae "pcie: add 
power indicator blink check").

--
Best regards,
Vladimir