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Re: [Qemu-ppc] [PATCH v3 05/33] Switch to new api in qdev/bus

From: David Gibson
Subject: Re: [Qemu-ppc] [PATCH v3 05/33] Switch to new api in qdev/bus
Date: Mon, 12 Aug 2019 20:36:33 +1000
User-agent: Mutt/1.12.1 (2019-06-15)

On Fri, Aug 09, 2019 at 01:39:46PM +0200, Cédric Le Goater wrote:
> >>> So.. is this change in the device_reset() signature really necessary?
> >>> Even if there are compelling reasons to handle warm reset in the new
> >>> API, that doesn't been you need to change device_reset() itself from
> >>> its established meaning of a cold (i.e. as per power cycle) reset.
> >>> Warm resets are generally called in rather more specific circumstances
> >>> (often under guest software direction) so it seems likely that users
> >>> would want to engage with the new reset API directly.  Or we could
> >>> just create a device_warm_reset() wrapper.  That would also avoid the
> >>> bare boolean parameter, which is not great for readability (you have
> >>> to look up the signature to have any idea what it means).
> >>
> >> I've added device_reset_cold/warm wrapper functions to avoid having to
> >> pass the boolean parameter. it seems I forgot to use them in qdev.c
> >> I suppose, like you said, we could live with
> >> + no function with the boolean parameter
> >> + device_reset doing cold reset
> >> + device_reset_warm (or device_warm_reset) for the warm version
> > 
> > Ok, good.
> > 
> > I'm afraid the whole series still makes me pretty uncomfortable,
> > though, since the whole "warm reset" concept still seems way to vague
> > to me.
> Isn't the reset after the CAS negotiation sequence between the hypervisor
> and the pseries machine some sort of warm reset driven by SW ?

Yes.. and?  The fact that something as messy as CAS can come under the
category of warm reset only re-inforces that what a warm reset is
isn't really well defined.

[That said, in the case of CAS, I'd really like it if we can change
things to avoid the pseudo-reset and just rewrite the dt instead.
The sorta-reboot causes us problems with -no-reboot and with disabling
the SLOF autoboot flag]

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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