netdev - Re: [PATCH V2 net 00/11] Extending the ena driver to support new features and enhance performance

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Date:   Tue, 04 Jun 2019 07:57:48 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     "Bshara, Nafea" <nafea@...zon.com>, Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "Jubran, Samih" <sameehj@...zon.com>,
        "Kiyanovski, Arthur" <akiyano@...zon.com>,
        "Bshara, Saeed" <saeedb@...zon.com>,
        "Tzalik, Guy" <gtzalik@...zon.com>,
        "Matushevsky, Alexander" <matua@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Wilson, Matt" <msw@...zon.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Belgazal, Netanel" <netanel@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>
Subject: Re: [PATCH V2 net 00/11] Extending the ena driver to support new
 features and enhance performance

On Tue, 2019-06-04 at 02:15 +0000, Bshara, Nafea wrote:
> Andrew,
> 
> Sent from my iPhone
> 
> On Jun 3, 2019, at 6:52 PM, Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > Any "SmartNIC" vendor has temptation of uAPI-level hand off to the
> > > firmware (including my employer), we all run pretty beefy processors
> > > inside "the NIC" after all.  The device centric ethtool configuration
> > > can be implemented by just forwarding the uAPI structures as they are
> > > to the FW.  I'm sure Andrew and others who would like to see Linux
> > > takes more control over PHYs etc. would not like this scenario, either.
> > 
> > No, i would not. There are a few good examples of both firmware and
> > open drivers being used to control the same PHY, on different
> > boards. The PHY driver was developed by the community, and has more
> > features than the firmware driver. And it keeps gaining features. The
> > firmware i stuck, no updates. The community driver can be debugged,
> > the firmware is a black box, no chance of the community fixing any
> > bugs in it.
> > 
> > And PHYs are commodity devices. I doubt there is any value add in the
> > firmware for a PHY, any real IPR which makes the product better, magic
> > sauce related to the PHY. So just save the cost of writing and
> > maintaining firmware, export the MDIO bus, and let Linux control it.
> > Concentrate the engineers on the interesting parts of the NIC, the
> > Smart parts, where there can be real IPR.
> > 
> > And i would say this is true for any NIC. Let Linux control the PHY.
> > 
> >      Andrew
> > 
> 
> It may be true for old GbE PHYs where it’s a discrete chip from the
> likes of Marvell or broadcom
> 
> But at 25/50/100G, the PHy is actually part of the nic. It’s a very
> complex SERDES.  Cloud providers like us spend enormous amount of
> time testing the PHY across process and voltage variations, all cable
> types, length and manufacturing variations, and against all switches
> we use.  Community drivers won’t be able to validate and tune all
> this.
> 
> Plus we would need exact same setting for Linux, including all
> distributions even 10year old like RHEL6, for all Windows, ESX, DPDK,
> FreeBSD,  and support millions of different customers with different
> sets of Machine images. 
> 
> In this case, there is no practical choice by have the firmware to
> manage the PHY

I don't quite know why we're talking about PHYs in this context.
ENA is basically a virtio NIC. It has no PHY.


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