netdev - RE: [PATCH net-next v4 RESEND] stmmac: tegra: Add MGBE support

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Date:   Wed, 12 Oct 2022 04:56:52 +0000
From:   Bhadram Varka <vbhadram@...dia.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <olteanv@...il.com>,
        Revanth Kumar Uppala <ruppala@...dia.com>
CC:     Jonathan Hunter <jonathanh@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next v4 RESEND] stmmac: tegra: Add MGBE support

Hi @Florian Fainelli,
Thanks for the review.

> -----Original Message-----
> From: Florian Fainelli <f.fainelli@...il.com>
> Sent: 27 September 2022 10:53 PM
> To: Thierry Reding <thierry.reding@...il.com>; David S . Miller
> <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>; Jakub
> Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>; Russell
> King <linux@...linux.org.uk>; Andrew Lunn <andrew@...n.ch>; Vladimir
> Oltean <olteanv@...il.com>
> Cc: Jonathan Hunter <jonathanh@...dia.com>; Bhadram Varka
> <vbhadram@...dia.com>; linux-tegra@...r.kernel.org;
> netdev@...r.kernel.org
> Subject: Re: [PATCH net-next v4 RESEND] stmmac: tegra: Add MGBE support
> 
> External email: Use caution opening links or attachments
> 
> 
> +Russell, Andrew, Vladimir,
> 
> On 9/23/22 04:49, Thierry Reding wrote:
> > From: Bhadram Varka <vbhadram@...dia.com>
> >
> > Add support for the Multi-Gigabit Ethernet (MGBE/XPCS) IP found on
> > NVIDIA Tegra234 SoCs.
> >
> > Signed-off-by: Bhadram Varka <vbhadram@...dia.com>
> > Signed-off-by: Thierry Reding <treding@...dia.com>
> > ---
> >   drivers/net/ethernet/stmicro/stmmac/Kconfig   |   6 +
> >   drivers/net/ethernet/stmicro/stmmac/Makefile  |   1 +
> >   .../net/ethernet/stmicro/stmmac/dwmac-tegra.c | 290
> > ++++++++++++++++++
> 
> You should be modeling this as a proper PCS driver and have a 'pcs-handle'
> property pointing to it in your Device Tree.
> 
> The configuration you are doing here is probably working the first time you
> bring-up the network device but I doubt it works across system
> suspend/resume states where power to the GMAC and PCS is lost, it also
> begs the question of which mediums this was tested with and whether
> dynamic switching of speeds and so on is working?
> --

For Tegra234, there is UPHY lanes control logic inside XPCS IP which is memory-mapped IP (not part of the MAC IP).
mgbe_uphy_lane_bringup performs UPHY lane bring up here. Here MGBE/XPCS works in XFI mode.

Agree that lane bring down logic is not present interface down/suspend paths. Will update the changes accordingly.
One more thing is that UPHY lane bring should happen only after the line side link is up. This also will make the changes.
Please let me know if I miss anything here.

Thanks,
Bhadram.