Re: [Qemu-devel] [PATCH v2 1/4] pc: append ssdt-misc.dsl to the DSDT

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 19, 2015 at 09:29:57PM +0200, Michael S. Tsirkin wrote:
> On Mon, Jan 19, 2015 at 06:26:55PM +0100, Paolo Bonzini wrote:
> > 
> > 
> > On 19/01/2015 18:14, Igor Mammedov wrote:
> > > I'm fine with moving "SMC out of the per-machine-type AML", should be
> > > a separate patch anyway. But patch-able SMC being in DSDT is our mistake
> > > that we allowed it to slip there and should be better moved to SSDT rather
> > > than staying in DSDT and making thing more complex.
> > > It's also candidate for trimming, i.e. dropping it from tables altogether
> > > if device is not present in QEMU, same applies to _S[34] Packages when
> > > respective features are disabled and to PEVT device template.
> > 
> > Yes, trimming is better than putting it in the DSDT, at least for simple
> > devices such as SMC and pvpanic.
> > 
> > >> > 
> > >>>> > >> simpler.  However, it also complicates backwards compatibility, so
> > >>>> > >> merge it with the DSDT.
> > >>> > > What are these complications?
> > >> > 
> > >> > The complication arises if we want to make the SSDT exactly the same for
> > >> > all QEMU versions, given a (machine type, command line) pair.  Then you
> > >> > either cannot do any change to ssdt-misc, or you have to keep different
> > >> > copies for each machine type.
> > > With resizable ROM blobs in master, there shouldn't be an issue with
> > > migration in new QEMU versions if size of SSDT changes.
> > 
> > There is only a very small issue that remains (the RSDP pointer is wrong
> > if the size changes),
> 
> Yes - for new machine types I'll send a patch to put it
> in memory.
> For old ones - there's a race, and it's painful to fix.  If we do want
> to try fixing it, one solution is to fail migration if attempted before
> rsdp is shadowed. Useful?
> 
> > so we probably should apply anyway the patch of
> > mine that allows the DSDT size to change; and we probably should pay
> > attention to SSDT, and version it.

Oh, missed that.
You mean this: "Add padding after the DSDT"?
Right but e.g. Igor's patches likely move RSDT anyway, no?

> > ("Let's just ignore the SSDT" was exactly what I feared when I disagreed
> > with putting in resizable ROM blobs first.  But now that it's in, I
> > cannot really argue otherwise).
> 
> I don't have a strong opinion here. you guys arrive
> at a rough consensus.:w
> 
> 
> > > So question is if we still need SSDT version-ing and per machine type
> > > SSDT compatibility? /it's better not to do version-ing at all if it could
> > > be avoided, due to maintenance headache it brings along/
> > 
> > I'm okay with re-evaluating that after your patches go in.
> > 
> > Paolo