linux-kernel - Re: [PATCH 01/20] net: phy: realtek: Fix events detection failure in LPI mode

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Message-ID: <8300d9ca-b877-860f-a975-731d6d3a93a5@gmail.com>
Date:   Mon, 8 Feb 2021 21:14:02 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King <linux@...linux.org.uk>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Vyacheslav Mitrofanov 
        <Vyacheslav.Mitrofanov@...kalelectronics.ru>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/20] net: phy: realtek: Fix events detection failure in
 LPI mode

On 08.02.2021 15:03, Serge Semin wrote:
> It has been noticed that RTL8211E PHY stops detecting and reporting events
> when EEE is successfully advertised and RXC stopping in LPI is enabled.
> The freeze happens right after 3.0.10 bit (PC1R "Clock Stop Enable"
> register) is set. At the same time LED2 stops blinking as if EEE mode has
> been disabled. Notably the network traffic still flows through the PHY
> with no obvious problem. Anyway if any MDIO read procedure is performed
> after the "RXC stop in LPI" mode is enabled PHY gets to be unfrozen, LED2
> starts blinking and PHY interrupts happens again. The problem has been
> noticed on RTL8211E PHY working together with DW GMAC 3.73a MAC and
> reporting its event via a dedicated IRQ signal. (Obviously the problem has
> been unnoticed in the polling mode, since it gets naturally fixed by the
> periodic MDIO read procedure from the PHY status register - BMSR.)
> 
> In order to fix that problem we suggest to locally re-implement the MMD
> write method for RTL8211E PHY and perform a dummy read right after the
> PC1R register is accessed to enable the RXC stopping in LPI mode.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> ---
>  drivers/net/phy/realtek.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
> index 99ecd6c4c15a..cbb86c257aae 100644
> --- a/drivers/net/phy/realtek.c
> +++ b/drivers/net/phy/realtek.c
> @@ -559,6 +559,42 @@ static int rtl822x_write_mmd(struct phy_device *phydev, int devnum, u16 regnum,
>  	return ret;
>  }
>  
> +static int rtl8211e_write_mmd(struct phy_device *phydev, int devnum, u16 regnum,
> +			      u16 val)
> +{
> +	int ret;
> +
> +	/* Write to the MMD registers by using the standard control/data pair.
> +	 * The only difference is that we need to perform a dummy read after
> +	 * the PC1R.CLKSTOP_EN bit is set. It's required to workaround an issue
> +	 * of a partial core freeze so LED2 stops blinking in EEE mode, PHY
> +	 * stops detecting the link change and raising IRQs until any read from
> +	 * its registers performed. That happens only if and right after the PHY
> +	 * is enabled to stop RXC in LPI mode.
> +	 */
> +	ret = __phy_write(phydev, MII_MMD_CTRL, devnum);
> +	if (ret)
> +		return ret;
> +
> +	ret = __phy_write(phydev, MII_MMD_DATA, regnum);
> +	if (ret)
> +		return ret;
> +
> +	ret = __phy_write(phydev, MII_MMD_CTRL, devnum | MII_MMD_CTRL_NOINCR);
> +	if (ret)
> +		return ret;
> +

Nice analysis. Alternatively to duplicating this code piece we could
export mmd_phy_indirect(). But up to you.

> +	ret = __phy_write(phydev, MII_MMD_DATA, val);
> +	if (ret)
> +		return ret;
> +
> +	if (devnum == MDIO_MMD_PCS && regnum == MDIO_CTRL1 &&
> +	    val & MDIO_PCS_CTRL1_CLKSTOP_EN)
> +		ret =  __phy_read(phydev, MII_MMD_DATA);
> +
> +	return ret < 0 ? ret : 0;
> +}
> +
>  static int rtl822x_get_features(struct phy_device *phydev)
>  {
>  	int val;
> @@ -725,6 +761,7 @@ static struct phy_driver realtek_drvs[] = {
>  		.resume		= genphy_resume,
>  		.read_page	= rtl821x_read_page,
>  		.write_page	= rtl821x_write_page,
> +		.write_mmd	= rtl8211e_write_mmd,
>  	}, {
>  		PHY_ID_MATCH_EXACT(0x001cc916),
>  		.name		= "RTL8211F Gigabit Ethernet",
>