netdev - Re: [PATCH net v2] r8169: fix rtl8125b PAUSE frames blasting when suspended

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Date: Thu, 30 Nov 2023 14:25:00 -0800
From: Jacob Keller <jacob.e.keller@...el.com>
To: Grant Grundler <grundler@...omium.org>
CC: ChunHao Lin <hau@...ltek.com>, <hkallweit1@...il.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>, <stable@...r.kernel.org>
Subject: Re: [PATCH net v2] r8169: fix rtl8125b PAUSE frames blasting when
 suspended



On 11/29/2023 3:40 PM, Grant Grundler wrote:
> On Wed, Nov 29, 2023 at 3:05 PM Jacob Keller <jacob.e.keller@...el.com> wrote:
>> On 11/29/2023 7:53 AM, ChunHao Lin wrote:
>>> When FIFO reaches near full state, device will issue pause frame.
>>> If pause slot is enabled(set to 1), in this time, device will issue
>>> pause frame only once. But if pause slot is disabled(set to 0), device
>>> will keep sending pause frames until FIFO reaches near empty state.
>>>
>>> When pause slot is disabled, if there is no one to handle receive
>>> packets, device FIFO will reach near full state and keep sending
>>> pause frames. That will impact entire local area network.
>>>
>>> This issue can be reproduced in 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.
>>>
>>> Fix this issue by enabling pause slot to only send pause frame once
>>> when FIFO reaches near full state.
>>>
>>
>> Makes sense. Avoiding the spam is good.  The naming is a bit confusing
>> but I guess that comes from realtek datasheet?
> 
> I don't know. It doesn't matter to me what it's called since I don't
> have access to the data sheet anyway. :/
> 

The name is fine, i just found it a bit hard to parse since its
effectively "PAUSE_SLOT_ON" makes us *not* send pause frames forever.

I think its fine as-is, since this is referring to the use of the pause
slot in hardware.

>>> Fixes: f1bce4ad2f1c ("r8169: add support for RTL8125")
>>> Reported-by: Grant Grundler <grundler@...omium.org>
>>> Tested-by: Grant Grundler <grundler@...omium.org>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: ChunHao Lin <hau@...ltek.com>
>>> ---
>>> v2:
>>> - update comment and title.
>>> ---
>>>  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 62cabeeb842a..bb787a52bc75 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)       /* 8125b and later */
>>
>> This confuses me though: RX_EARLY_OFF is (1 << 11) as well.. Is that
>> from a different set of devices?
> 
> Yes, for a different HW version of the device.
> 

Great.

>> We're writing to the same register
>> RxConfig here I think in both cases?
> 
> Yes. But to different versions of the HW which use this bit
> differently. Ergo the comment about "8125b and later".
> 
>> Can you clarify if these are supposed to be the same bit?
> 
> Yes, they are the same bit - but different versions of HW use BIT(11)
> differently.

Thanks for the clarification!

> 
>>
>>>  #define      RXCFG_DMA_SHIFT                 8
>>>                                       /* Unlimited maximum PCI burst. */
>>>  #define      RX_DMA_BURST                    (7 << RXCFG_DMA_SHIFT)
>>> @@ -2306,9 +2307,13 @@ 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;
>>
>> I assume there isn't a VER_62 between these?
> 
> Correct. My clue is this code near the top of this file:
> 
>  149         [RTL_GIGA_MAC_VER_61] = {"RTL8125A",            FIRMWARE_8125A_3},
>  150         /* reserve 62 for CFG_METHOD_4 in the vendor driver */
>  151         [RTL_GIGA_MAC_VER_63] = {"RTL8125B",            FIRMWARE_8125B_2},
> 
>>
>>> +     case RTL_GIGA_MAC_VER_63:
>>> +             RTL_W32(tp, RxConfig, RX_FETCH_DFLT_8125 | RX_DMA_BURST |
>>> +                     RX_PAUSE_SLOT_ON);
>>
>> We add RX_PAUSE_SLOT_ON now for RTL_GIGA_MAC_VER_63 in addition. Makes
>> sense.
> 
> Exactly.
> 
> thanks for reviewing!
> 

Great.

For the record:

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>