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Re: [PATCH v2 10/12] hw/block/nvme: move cmb logic to v1.4


From: Klaus Jensen
Subject: Re: [PATCH v2 10/12] hw/block/nvme: move cmb logic to v1.4
Date: Mon, 18 Jan 2021 20:23:30 +0100

On Jan 18 14:22, Klaus Jensen wrote:
> On Jan 18 22:12, Minwoo Im wrote:
> > On 21-01-18 14:10:50, Klaus Jensen wrote:
> > > On Jan 18 22:09, Minwoo Im wrote:
> > > > > > Yes, CMB in v1.4 is not backward-compatible, but is it okay to move 
> > > > > > onto
> > > > > > the CMB v1.4 from v1.3 without supporting the v1.3 usage on this 
> > > > > > device
> > > > > > model?
> > > > > 
> > > > > Next patch moves to v1.4. I wanted to split it because the "bump" 
> > > > > patch
> > > > > also adds a couple of other v1.4 requires fields. But I understand 
> > > > > that
> > > > > this is slightly wrong.
> > > > 
> > > > Sorry, I meant I'd like to have CMB for v1.3 support along with the v1.4
> > > > support in this device model separately.  Maybe I missed the linux-nvme
> > > > mailing list for CMB v1.4, but is there no plan to keep supportin CMB
> > > > v1.3 in NVMe driver?
> > > 
> > > I posted a patch on linux-nvme for v1.4 support in the kernel. It will
> > > support both the v1.3 and v1.4 behavior :)
> > 
> > Then, can we maintain CMB v1.3 also in QEMU also along with v1.4 ? :)
> 
> My first version of this patch actually included compatibility support
> for v1.3 ("legacy cmb"), but Keith suggested we just drop that and keep
> this device compliant.
> 
> What we could do is allow the spec version to be chosen with a
> parameter?

Uhm. Maybe not. I gave this some more thought.

Adding a device parameter to choose the specification version requires
us to maintain QEMU "compat" properties across different QEMU version.
I'm not sure we want that for something like this.

Maybe the best course of action actually *is* an 'x-legacy-cmb'
parameter.

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