netdev - Re: [PATCH] net: thunderx: add support for rgmii internal delay

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Date:   Wed, 13 Dec 2017 12:10:54 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     Sunil Goutham <sgoutham@...ium.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: thunderx: add support for rgmii internal delay

> +void xcv_init_hw(int phy_mode)
>  {
>  	u64  cfg;
>  
> @@ -81,12 +81,31 @@ void xcv_init_hw(void)
>  	/* Wait for DLL to lock */
>  	msleep(1);
>  
> -	/* Configure DLL - enable or bypass
> -	 * TX no bypass, RX bypass
> -	 */
> +	/* enable/bypass DLL providing MAC based internal TX/RX delays */
>  	cfg = readq_relaxed(xcv->reg_base + XCV_DLL_CTL);
> -	cfg &= ~0xFF03;
> -	cfg |= CLKRX_BYP;
> +	cfg &= ~0xffff00;
> +	switch (phy_mode) {
> +	/* RX and TX delays are added by the MAC */
> +	case PHY_INTERFACE_MODE_RGMII:
> +		break;
> +	/* internal RX and TX delays provided by the PHY */
> +	case PHY_INTERFACE_MODE_RGMII_ID:
> +		cfg |= CLKRX_BYP;
> +		cfg |= CLKTX_BYP;
> +		break;
> +	/* internal RX delay provided by the PHY, the MAC
> +	 * should not add an RX delay in this case
> +	 */
> +	case PHY_INTERFACE_MODE_RGMII_RXID:
> +		cfg |= CLKRX_BYP;
> +		break;
> +	/* internal TX delay provided by the PHY, the MAC
> +	 * should not add an TX delay in this case
> +	 */
> +	case PHY_INTERFACE_MODE_RGMII_TXID:
> +		cfg |= CLKRX_BYP;
> +		break;
> +	}

Hi Tim

This i don't get. Normally, you leave the PHY to handle delays, if
needed. The MAC should not add any. Here you seem to assume a delay is
always needed, and if the PHY is not providing it, the MAC should.

       Andrew