netdev - Re: [PATCH net 1/2] r8169: enable rtl8125b pause slot

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Date: Mon, 27 Nov 2023 12:28:21 -0800
From: Grant Grundler <grundler@...omium.org>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: ChunHao Lin <hau@...ltek.com>, nic_swsd@...ltek.com, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, grundler@...omium.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH net 1/2] r8169: enable rtl8125b pause slot

On Mon, Nov 27, 2023 at 12:03 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>
> On 27.11.2023 18:57, ChunHao Lin wrote:
> > 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.

The comment is correct but should mention that this is true after a
suspend. In other words, when an idle device goes into a lower power
state, eventually the NIC will start blasting PAUSE frames on the
local network.

I was able to reproduce the problem very easily with a recent
Chromebox (not Chromebook) in developer mode running a test image (and
v5.10 kernel):
1) ping -f $CHROMEBOX (from workstation on same local network)
2) run "powerd_dbus_suspend" from command line on the $CHROMEBOX
3) ping $ROUTER (wait until ping fails from workstation)

Takes about ~20-30 seconds after step 2 for the local network to stop working.
At that point, tcpdump from the workstation is full of PAUSE frames.

I did not check that WOL still works.

The exact patches I used on chromeos-5.10 kernel branch are publicly
visible here:
    https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/5056381

> > 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.
>
> > Fixes: f1bce4ad2f1c ("r8169: add support for RTL8125")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: ChunHao Lin <hau@...ltek.com>

Tested-by: Grant Grundler <grundler@...omium.org>
Reviewed-by: Grant Grundler <grundler@...omiuim.org>

(adding my reviewed-by to indicate I think the code is fine... I
appreciate Heiner asking for better comments though.)

cheers,
grant

> > ---
> >  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.
>
> >  #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;
>