Re: [Qemu-devel] [Qemu-block] [PATCH] nvme: do not advertise support for unsupported arbitration mechanism

[Maxim Levitsky <mlevitsk@redhat.com>]

On Fri, 2019-06-14 at 22:39 +0200, Max Reitz wrote:
> On 06.06.19 11:25, Klaus Birkelund Jensen wrote:
> > The device mistakenly reports that the Weighted Round Robin with Urgent
> > Priority Class arbitration mechanism is supported.
> > 
> > It is not.
> 
> I believe you based on the fact that there is no “weight” or “priority”
> anywhere in nvme.c, and that it does not evaluate the Arbitration
> Mechanism Selected field.
> 
> > Signed-off-by: Klaus Birkelund Jensen <klaus.jensen@cnexlabs.com>
> > ---
> >  hw/block/nvme.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index 30e50f7a3853..415b4641d6b4 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -1383,7 +1383,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
> >      n->bar.cap = 0;
> >      NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);
> >      NVME_CAP_SET_CQR(n->bar.cap, 1);
> > -    NVME_CAP_SET_AMS(n->bar.cap, 1);
> 
> I suppose the better way would be to pass 0, so it is more explicit, I
> think.
> 
> (Just removing it looks like it may have just been forgotten.)
> 
> Max
> 
> >      NVME_CAP_SET_TO(n->bar.cap, 0xf);
> >      NVME_CAP_SET_CSS(n->bar.cap, 1);
> >      NVME_CAP_SET_MPSMAX(n->bar.cap, 4);
> > 
> 
> 

Yea. no way that this driver supports WRRU and I haven't noticed it.
Just checked again to be sure.

To be honest, after some quick look, 
that driver doesn' even really support the regular Round-Robin as it uses a timer to process a specific queue, 
kicked up by a doorbell write :-)


Acked-by: Maxim Levitsky <mlevitsk@redhat.com>


Best regards,
	Maxim Levitsky