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Date:   Thu, 22 Nov 2018 20:28:37 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Quentin Schulz <quentin.schulz@bootlin.com>
Cc:     davem@davemloft.net, f.fainelli@gmail.com,
        allan.nielsen@microchip.com, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, thomas.petazzoni@bootlin.com,
        alexandre.belloni@bootlin.com
Subject: Re: [PATCH net] net: phy: mscc: fix deadlock in
 vsc85xx_default_config
Message-ID: <20181122192837.GH10697@lunn.ch>
References: <20181122131232.32032-1-quentin.schulz@bootlin.com>
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On Thu, Nov 22, 2018 at 02:12:32PM +0100, Quentin Schulz wrote:
> The vsc85xx_default_config function called in the vsc85xx_config_init
> function which is used by VSC8530, VSC8531, VSC8540 and VSC8541 PHYs
> mistakenly calls phy_read and phy_write in-between phy_select_page and
> phy_restore_page.
> 
> phy_select_page and phy_restore_page actually take and release the MDIO
> bus lock so __phy_write and __phy_read (which assume that you already
> have the MDIO bus lock unlike phy_write and phy_read) should be used for
> any call in between the two said functions.
> 
> Let's fix this deadlock.
> 
> Fixes: 6a0bfbbe20b0 ("net: phy: mscc: migrate to phy_select/restore_page functions")
> 
> Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
> ---
>  drivers/net/phy/mscc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/mscc.c b/drivers/net/phy/mscc.c
> index 62269e578718..6856fe4d1a60 100644
> --- a/drivers/net/phy/mscc.c
> +++ b/drivers/net/phy/mscc.c
> @@ -814,10 +814,10 @@ static int vsc85xx_default_config(struct phy_device *phydev)
>  	if (rc < 0)
>  		goto out_unlock;
>  
> -	reg_val = phy_read(phydev, MSCC_PHY_RGMII_CNTL);
> +	reg_val = __phy_read(phydev, MSCC_PHY_RGMII_CNTL);
>  	reg_val &= ~(RGMII_RX_CLK_DELAY_MASK);
>  	reg_val |= (RGMII_RX_CLK_DELAY_1_1_NS << RGMII_RX_CLK_DELAY_POS);
> -	phy_write(phydev, MSCC_PHY_RGMII_CNTL, reg_val);
> +	__phy_write(phydev, MSCC_PHY_RGMII_CNTL, reg_val);

Hi Quentin

You appear to be only accessing a single register, read/modify/write.
I think you can use phy_modify_paged(), which will take care of all
the locking for you.

    Andrew