Subject: Re: [PATCH net v2] net: stmmac: Set MAC's flow control register to reflect current settings

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 22 Nov 2022 18:40:33 +0000

On Tue, Nov 22, 2022 at 02:39:35PM +0800, Goh, Wei Sheng wrote:
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> index c25bfecb4a2d..369db308b1dd 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> @@ -748,6 +748,9 @@ static void dwmac4_flow_ctrl(struct mac_device_info *hw, unsigned int duplex,
>  	if (fc & FLOW_RX) {
>  		pr_debug("\tReceive Flow-Control ON\n");
>  		flow |= GMAC_RX_FLOW_CTRL_RFE;
> +	} else {
> +		pr_debug("\tReceive Flow-Control OFF\n");
> +		flow &= ~GMAC_RX_FLOW_CTRL_RFE;
>  	}
>  	writel(flow, ioaddr + GMAC_RX_FLOW_CTRL);

This doesn't look correct to me. The function starts off:

        unsigned int flow = 0;

flow is not written to before the context above. So, the code you've
added effectively does:

	flow = 0 & ~GMAC_RX_FLOW_CTRL_RFE;

which is still zero. So, I don't think this hunk is meaningful apart
from adding the pr_debug().

> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 8273e6a175c8..ab7f48f32f5b 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1061,8 +1061,16 @@ static void stmmac_mac_link_up(struct phylink_config *config,
>  		ctrl |= priv->hw->link.duplex;
>  
>  	/* Flow Control operation */
> -	if (tx_pause && rx_pause)
> -		stmmac_mac_flow_ctrl(priv, duplex);
> +	if (rx_pause && tx_pause)
> +		priv->flow_ctrl = FLOW_AUTO;
> +	else if (rx_pause && !tx_pause)
> +		priv->flow_ctrl = FLOW_RX;
> +	else if (!rx_pause && tx_pause)
> +		priv->flow_ctrl = FLOW_TX;
> +	else
> +		priv->flow_ctrl = FLOW_OFF;
> +
> +	stmmac_mac_flow_ctrl(priv, duplex);
>  
>  	if (ctrl != old_ctrl)
>  		writel(ctrl, priv->ioaddr + MAC_CTRL_REG);

This looks like the true fix for correctly setting the flow control
depending on the phylink link_up() (which will contain the resuts of
pause negotiation, rate adaption or overriden by ethtool - but only
when operating in full duplex mode.)

-- 
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