linux-kernel - Re: [net: PATCH] net: mvpp2: disable link IRQ waiting for IDLE frames

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Date:   Thu, 28 Feb 2019 14:58:42 +0100
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        netdev <netdev@...r.kernel.org>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        Grégory Clement <gregory.clement@...tlin.com>,
        nadavh@...vell.com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [net: PATCH] net: mvpp2: disable link IRQ waiting for IDLE frames

Hi Russell,

czw., 28 lut 2019 o 10:36 Russell King - ARM Linux admin
<linux@...linux.org.uk> napisał(a):
>
> On Wed, Feb 27, 2019 at 06:47:32PM +0100, Marcin Wojtas wrote:
> > Current version of the driver was configuring XLG MAC
> > in a way to wait 3 IDLE frames before allowing for the
> > link-up interrupt to be triggered. This resulted in an
> > issue, preventing to detect the link change during RX
> > traffic on the interface. Fix that.
>
> What about noise sensitivity?  Does this now mean that on boards such as
> Macchiatobin Single Shot or Clearfog GT9k where the serdes is connected
> directly to a SFP cage, that noise on the serdes lines triggers a link
> indication?
>

Afaik waiting for idle frames is not required by any standard. In fact
this feature of the XLG MAC caused a risk that after dropping the link
during data transfer it would never go up again until remote peer
stops it.

I tested it on 3 different boards with SerDes directly connected to
the SFP cage and I'm also not aware of any reporte about
noise-triggered false link interrupts in XLG MAC (proprietary Marvell
mvpp2x driver did not use waiting 3 idle frames feature). I'd rather
assume the MAC is not vulnerable to it, and only properly established
link can trigger an event.

Best regards,
Marcin

> >
> > Fixes: 4bb043262878 ("net: mvpp2: phylink support")
> > Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
> > ---
> >  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > index 16066c2..f1378f9 100644
> > --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > @@ -4532,8 +4532,7 @@ static void mvpp2_xlg_config(struct mvpp2_port *port, unsigned int mode,
> >               ctrl0 |= MVPP22_XLG_CTRL0_RX_FLOW_CTRL_EN;
> >
> >       ctrl4 &= ~MVPP22_XLG_CTRL4_MACMODSELECT_GMAC;
> > -     ctrl4 |= MVPP22_XLG_CTRL4_FWD_FC | MVPP22_XLG_CTRL4_FWD_PFC |
> > -              MVPP22_XLG_CTRL4_EN_IDLE_CHECK;
> > +     ctrl4 |= MVPP22_XLG_CTRL4_FWD_FC | MVPP22_XLG_CTRL4_FWD_PFC;
> >
> >       writel(ctrl0, port->base + MVPP22_XLG_CTRL0_REG);
> >       writel(ctrl4, port->base + MVPP22_XLG_CTRL4_REG);
> > --
> > 2.7.4
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up

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