netdev - Re: [pull request][net-next V10 00/14] Add mlx5 subfunction support

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Message-ID: <20210125194941.GZ4147@nvidia.com>
Date:   Mon, 25 Jan 2021 15:49:41 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Edwin Peer <edwin.peer@...adcom.com>
CC:     Parav Pandit <parav@...dia.com>, Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        David Ahern <dsahern@...nel.org>,
        Kiran Patil <kiran.patil@...el.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        "Ertman, David M" <david.m.ertman@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [pull request][net-next V10 00/14] Add mlx5 subfunction support

On Mon, Jan 25, 2021 at 11:23:56AM -0800, Edwin Peer wrote:
> On Mon, Jan 25, 2021 at 5:22 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > SRIOV and SF's require a simple linear lookup to learn the "function"
> > because the BAR space is required to be linear.
> 
> Isn't this still true even for NumVF's > 256? Wouldn't there still be
> a contiguous VF BAR space? Don't the routing IDs simply carry on
> incrementing by stride, with each being assigned the next slice of the
> shared BAR space?

I've never seen someone implement a NumVF > 256 by co-opting the bus
number.

Can Linux even assign more bus numbers to a port without firmware
help? Bus numbers are something that requires the root complex to be
aware of to setup routability.

Jason