Re: [virtio-comment] Re: [PATCH 3/3] shared memory: Define mmio registers

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: virtio-comment@lists.oasis-open.org
Subject: Re: [virtio-comment] Re: [PATCH 3/3] shared memory: Define mmio registers
Date: Wed, 13 Feb 2019 16:52:30 +0000	[thread overview]
Message-ID: <20190213165230.GE2601@work-vm> (raw)
In-Reply-To: <20190213023352.GD14307@stefanha-x1.localdomain>

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> On Fri, Jan 11, 2019 at 11:42:00AM +0000, Dr. David Alan Gilbert (git) wrote:
> > diff --git a/content.tex b/content.tex
> > index 776162a..e2435ff 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -1641,6 +1641,33 @@ All register values are organized as Little Endian.
> >      selected by writing to \field{QueueSel}.
> >    }
> >    \hline 
> > +  \mmioreg{SHMSel}{Shared memory region select}{0x0b0}{W}{%
> > +    Writing to this register selects the shared memory region \ref{sec:Basic Facilities of a Virtio Device / Shared Memory Regions}
> > +    following operations on \field{SHMId}, \field{SHMLenLow}, \field{SHMLenHigh},
> > +    \field{SHMBaseLow} and \field{SHMBaseHigh} apply to. The index
> > +    number of the first region is zero (0x0); note that it is a
> > +    simple index that does not correspond to the \field{id}.
> 
> Why use a separate virtio-mmio index instead of the shared memory ID?
> The driver would map those IDs it knows about, so I'm not sure if
> enumerating them via a separate index is useful.  Plus using the ID lets
> you drop one register from the interface.

Yes, I think if we don't need enumeration that's right; we just shange
SHMId to be the writeable register and drop the SHMSel register.

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

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