Re: [virtio-comment] [PATCH v4] virtio-i2c: add the device specification

[Gerd Hoffmann <kraxel@redhat.com>]

On Tue, Nov 17, 2020 at 02:55:14PM +0800, Jie Deng wrote:
> 
> On 2020/11/16 16:16, Paolo Bonzini wrote:
> > On 16/11/20 03:12, Jie Deng wrote:
> > > Fore example, the frontend may kick the sequence "write read read
> > > ..." to the backend at a time.
> > > 
> > > The segments can be aggregated into "i2c_msg list" and sent to the
> > > hardware at a time by the backend.
> > > 
> > > The host native drivers will finally send these segments using the
> > > methods they support.
> > 
> > If so, the spec needs to specify what the backend must/should/may
> > aggregate into a single host-side transaction.
> > 
> > What my proposal does is essentially saying that the backend MUST
> > aggregate a write and a read segment into a single transaction if it is
> > sent with a single virtio-i2c request.
> > 
> > Paolo
> > 
> This may depend on the host hardware. I can add a host feature bit to
> indicate it.

That is not enough.  You also need that for the transactions.  If the
driver sends a write and a read message the device needs to know
whenever that is one or two transactions.  So if you want continue
with the i2c_msg list idea you need some way to group your messages
into transactions.

Or you go with paolos idea which looks simpler to me.

take care,
  Gerd