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

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Date: Mon, 27 Nov 2023 21:03:45 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: ChunHao Lin <hau@...ltek.com>
Cc: 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 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.
> 
> 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>
> ---
>  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;