On Fri, Sep 16, 2011 at 12:41:40PM +0200, Paolo Bonzini wrote:
> On 09/16/2011 05:06 AM, David Gibson wrote:
> >>>
> >>> 1) do you mean, in Linux terms, one target per SCSI _host_ or one
> >>> target per SCSI _channel_? i.e. if you looks at
> >>> /sys/bus/scsi/devices, right now it looks like
> >>>
> >>> 0:0:0:0 0:0:1:0 (two targets on the same host and channel)
> >>>
> >>> Should it be?
> >>>
> >>> 0:0:0:0 0:1:0:0 (one target per channel)
> >>>
> >>> or
> >>>
> >>> 0:0:0:0 1:0:0:0 (one target per host)
> >>>
> >>> If it is the former, then you are simply hitting a limitation of the
> >>> SCSI layer in QEMU and I do have patches to make assignment more
> >>> flexible. Based on the Linux VSCSI driver, and based on what SLOF
> >>> does, I'd guess that's what you mean.
> >
> >Well, now I'm confused. I had a look at a pHyp machine, and Linux
> >seemed to see it as multiple targets on a single channel, but I'm sure
> >the PAPR spec says you shouldn't have that. So I'm going to have to
> >look closer now.
>
> If this is the case, there might be a bug in SLOF's probing of SCSI
> devices.
Um.. I'm confused. This is a pHyp (aka PowerVM) machine, so there is
no SLOF. What I'm seeing there seems to contradict the PAPR spec
which is supposed to describe it. So I don't see how it has a bearing
on SLOF addressing.
> SLOF probes target 0/LUN 0 on eight channels, i.e. from 0:0:0 to
> 7:0:0. Linux however shows them the same as pHyp, i.e. from 0:0:0
> to 0:7:0.
>
> The reason this works is because LUN parsing in QEMU is completely
> broken (by Ben's admission in spapr_vscsi.c :)) and so SLOF's x:0:0
> and Linux's 0:x:0 end up referring to the same device.
>
> Now, when implementing SCSI addressing I had two choices:
>
> (1) leave them where Linux sees them. This seems correct according
> to your experiments with pHyp, but then SLOF could only see 0:0:0;
>
> (2) move the devices so that both SLOF and Linux see them as x:0:0
> (one target per channel). This would be inconsistent with pHyp, but
> it doesn't break either SLOF or Linux.
>
> So, I would like to agree on a plan for merging the SCSI addressing
> series. Right now I am doing (2), because it lets me use the
> current version of SLOF. Is it okay for you to merge the feature
> with these semantics?
(2) sounds like what PAPR describes to me, so that sounds fine to me.
But I still don't follow your reasoning leading up to that.
> If you want to change to (1), that can be done easily. However, it
> requires fixing SLOF, so it would have to go preferably through
> Alex's PPC tree.
>
> (Again, that would be just the defaults---the addressing can always
> be overridden by using -device explicitly).
>
> Paolo
>
--
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_!
http://www.ozlabs.org/~dgibson
