netdev - Re: [PATCH net-next 1/2] net: usb: lan78xx: Fixup EEE

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Message-ID: <ZhLc6W2TS9_vWOeq@pengutronix.de>
Date: Sun, 7 Apr 2024 19:50:33 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: Woojung Huh <woojung.huh@...rochip.com>, UNGLinuxDriver@...rochip.com,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Bryan Whitehead <bryan.whitehead@...rochip.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] net: usb: lan78xx: Fixup EEE

Hi Andrew,

On Sat, Apr 06, 2024 at 03:15:59PM -0500, Andrew Lunn wrote:
.....
> ---
> -	if (edata->eee_enabled) {
> -		ret = lan78xx_read_reg(dev, MAC_CR, &buf);
> -		buf |= MAC_CR_EEE_EN_;
> -		ret = lan78xx_write_reg(dev, MAC_CR, buf);
> -
> -		phy_ethtool_set_eee(net->phydev, edata);
> -
> -		buf = (u32)edata->tx_lpi_timer;
> -		ret = lan78xx_write_reg(dev, EEE_TX_LPI_REQ_DLY, buf);
> -	} else {
> -		ret = lan78xx_read_reg(dev, MAC_CR, &buf);
> -		buf &= ~MAC_CR_EEE_EN_;
> -		ret = lan78xx_write_reg(dev, MAC_CR, buf);
> -	}
> +	ret = phy_ethtool_set_eee(net->phydev, edata);
> +	if (ret < 0)
> +		goto out;
>  
> +	buf = (u32)edata->tx_lpi_timer;
> +	ret = lan78xx_write_reg(dev, EEE_TX_LPI_REQ_DLY, buf);

According to the documentation:
"Host software should only change this field when Energy Efficient
Ethernet Enable (EEEEN) is cleared."

Even more: "A value of zero may adversely affect the ability of the TX
data path to support Gigabit operation. A reasonable value when the part
is operating at Gigabit speeds is 50 us."

Previous code seems to not care about it too. So, it would be not a
regression if something is broken.

Reviewed-by: Oleksij Rempel <o.rempel@...gutronix.de>

I'll get some time to work on this driver in some months, in this case
I'll take a closer look on EEE too.

Regards,
Oleksij
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