linux-kernel - Re: [EXT] Re: [PATCH RFC net-next 03/19] net: mvpp2: add CM3 SRAM memory map

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Date:   Sun, 10 Jan 2021 18:27:26 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Stefan Chulski <stefanc@...vell.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mw@...ihalf.com" <mw@...ihalf.com>,
        "atenart@...nel.org" <atenart@...nel.org>
Subject: Re: [EXT] Re: [PATCH RFC net-next  03/19] net: mvpp2: add CM3 SRAM
 memory map

On Sun, Jan 10, 2021 at 06:09:39PM +0000, Stefan Chulski wrote:
> > > > > +	} else {
> > > > > +		priv->sram_pool = of_gen_pool_get(dn, "cm3-mem", 0);
> > > > > +		if (!priv->sram_pool) {
> > > > > +			dev_warn(&pdev->dev, "DT is too old, TX FC
> > > > disabled\n");
> > > >
> > > > I don't see anything in this patch that disables TX flow control,
> > > > which means this warning message is misleading.
> > >
> > > OK, I would change to TX FC not supported.
> > 
> > And you should tell phlylink, so it knows to disable it in autoneg.
> > 
> > Which make me wonder, do we need a fix for stable? Has flow control never
> > been support in this device up until these patches get merged?
> > It should not be negotiated if it is not supported, which means telling phylink.
> > 
> >    Andrew
> 
> TX FC never were really supported. MAC or PHY can negotiated flow control.
> But MAC would never trigger FC frame.

That really sucks.

> Should I prepare separate patch that disable TX FC till we merge this patches?

>From what I see in table 28B in 802.3, there is no way to advertise
that you only support RX flow control. If you advertise ASM_DIR=1
PAUSE=0, it basically means you support sending FC frames, but not
receiving them. Advertising anything with PAUSE=1 means you support
both sending and receiving FC frames, irrespective of the state of
ASM_DIR.

So, our only option would be to completely disable pause frames.
Yes, I think we need a separate patch for that for the net tree,
and it should be backported to stable kernels, IMHO.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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