linux-kernel - RE: [PATCH net 1/2] r8169: enable rtl8125b pause slot

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Date:   Wed, 29 Nov 2023 15:08:11 +0000
From:   Hau <hau@...ltek.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
CC:     nic_swsd <nic_swsd@...ltek.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "grundler@...omium.org" <grundler@...omium.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH net 1/2] r8169: enable rtl8125b pause slot

> > When FIFO reach near full state, device will issue pause frame.
> > If pause slot is enabled(set to 1), in this time, device will issue
> > pause frame once. But if pause slot is disabled(set to 0), device will
> > keep sending pause frames until FIFO reach near empty state.
> >
> > When pause slot is disabled, if there is no one to handle receive
> > packets (ex. unexpected shutdown), device FIFO will reach near full
> > state and keep sending pause frames. That will impact entire local
> > area network.
> >
> > In this patch default enable pause slot to prevent this kind of
> > situation.
> >
> Can this change have any side effect? I'm asking because apparently the hw
> engineers had a reason to make the behavior configurable.

It should not have any side effect. This setting is also used in Realtek driver.

> > Fixes: f1bce4ad2f1c ("r8169: add support for RTL8125")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: ChunHao Lin <hau@...ltek.com>
> > ---
> >  drivers/net/ethernet/realtek/r8169_main.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/realtek/r8169_main.c
> > b/drivers/net/ethernet/realtek/r8169_main.c
> > index 295366a85c63..473b3245754f 100644
> > --- a/drivers/net/ethernet/realtek/r8169_main.c
> > +++ b/drivers/net/ethernet/realtek/r8169_main.c
> > @@ -196,6 +196,7 @@ enum rtl_registers {
> >                                       /* No threshold before first PCI xfer */
> >  #define      RX_FIFO_THRESH                  (7 << RXCFG_FIFO_SHIFT)
> >  #define      RX_EARLY_OFF                    (1 << 11)
> > +#define      RX_PAUSE_SLOT_ON                (1 << 11)
> 
> Depending on the chip version this bit has different meanings. Therefore it
> would be good to add a comment that RX_PAUSE_SLOT_ON is specific to
> RTL8125B.

I will do that and submit again.

> >  #define      RXCFG_DMA_SHIFT                 8
> >                                       /* Unlimited maximum PCI burst. */
> >  #define      RX_DMA_BURST                    (7 << RXCFG_DMA_SHIFT)
> > @@ -2305,9 +2306,13 @@ static void rtl_init_rxcfg(struct rtl8169_private
> *tp)
> >       case RTL_GIGA_MAC_VER_40 ... RTL_GIGA_MAC_VER_53:
> >               RTL_W32(tp, RxConfig, RX128_INT_EN | RX_MULTI_EN |
> RX_DMA_BURST | RX_EARLY_OFF);
> >               break;
> > -     case RTL_GIGA_MAC_VER_61 ... RTL_GIGA_MAC_VER_63:
> > +     case RTL_GIGA_MAC_VER_61:
> >               RTL_W32(tp, RxConfig, RX_FETCH_DFLT_8125 | RX_DMA_BURST);
> >               break;
> > +     case RTL_GIGA_MAC_VER_63:
> > +             RTL_W32(tp, RxConfig, RX_FETCH_DFLT_8125 | RX_DMA_BURST |
> > +                     RX_PAUSE_SLOT_ON);
> > +             break;
> >       default:
> >               RTL_W32(tp, RxConfig, RX128_INT_EN | RX_DMA_BURST);
> >               break;