netdev - Re: [PATCH] phy: realtek: use new helpers for paged register access

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Message-ID: <20180112210107.GA7470@lunn.ch>
Date:   Fri, 12 Jan 2018 22:01:07 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] phy: realtek: use new helpers for paged register access

On Fri, Jan 12, 2018 at 09:30:08PM +0100, Heiner Kallweit wrote:
> Make use of the new helpers for paged register access.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/phy/realtek.c | 59 +++++++++++------------------------------------
>  1 file changed, 14 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
> index 7c1bf688d..887bad07a 100644
> --- a/drivers/net/phy/realtek.c
> +++ b/drivers/net/phy/realtek.c
> @@ -41,37 +41,14 @@ MODULE_DESCRIPTION("Realtek PHY driver");
>  MODULE_AUTHOR("Johnson Leung");
>  MODULE_LICENSE("GPL");
>  
> -static int rtl8211x_page_read(struct phy_device *phydev, u16 page, u16 address)
> +static int rtl821x_read_page(struct phy_device *phydev)
>  {
> -	int ret;
> -
> -	ret = phy_write(phydev, RTL821x_PAGE_SELECT, page);
> -	if (ret)
> -		return ret;
> -
> -	ret = phy_read(phydev, address);
> -
> -	/* restore to default page 0 */
> -	phy_write(phydev, RTL821x_PAGE_SELECT, 0x0);
> -
> -	return ret;
> +	return phy_read(phydev, RTL821x_PAGE_SELECT);

Hi Heiner

It think this is wrong. You need to use __phy_read(). phy_read() does
an mdiobus_read(), which takes the bus->mdio_lock. However,

int phy_save_page(struct phy_device *phydev)
{
        mutex_lock(&phydev->mdio.bus->mdio_lock);
        return __phy_read_page(phydev);
}

This also takes the same lock. So this should deadlock.

Try turning on CONFIG_PROVE_LOCKING, it will detect problems like
this.

	Andrew