netdev - Re: [net-next V9 14/14] net/mlx5: Add devlink subfunction port documentation

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Date:   Thu, 21 Jan 2021 20:11:57 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
CC:     Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <alexander.duyck@...il.com>,
        <edwin.peer@...adcom.com>, <dsahern@...nel.org>,
        <kiran.patil@...el.com>, <jacob.e.keller@...el.com>,
        <david.m.ertman@...el.com>, <dan.j.williams@...el.com>,
        Parav Pandit <parav@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [net-next V9 14/14] net/mlx5: Add devlink subfunction port
 documentation

On Thu, Jan 21, 2021 at 12:59:55PM -0800, Samudrala, Sridhar wrote:

> > +                 mlx5_core.sf.4
> > +          (subfunction auxiliary device)
> > +                       /\
> > +                      /  \
> > +                     /    \
> > +                    /      \
> > +                   /        \
> > +      mlx5_core.eth.4     mlx5_core.rdma.4
> > +     (sf eth aux dev)     (sf rdma aux dev)
> > +         |                      |
> > +         |                      |
> > +      p0sf88                  mlx5_0
> > +     (sf netdev)          (sf rdma device)
> 
> This picture seems to indicate that when SF is activated, a sub
> function auxiliary device is created 

Yes

> and when a driver is bound to that sub function aux device and
> probed, 2 additional auxiliary devices are created.  

More than two, but yes

> Is this correct? Are all these auxiliary devices seen on the same
> aux bus?  

Yes

> Why do we need another sf eth aux device?

The first aux device represents the physical HW and mlx5_core binds to it,
the analog is like a pci_device.

The other aux devices represent the subsystem split of the mlx5 driver
- mlx5_core creates them and each subsystem in turn binds to the
mlx5_core driver. This already exists, and Intel will be doing this as
well whenever the RDMA driver is posted again..

Jason