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Date:   Thu, 10 Oct 2019 21:26:38 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Marek Vasut <marex@...x.de>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        George McCollister <george.mccollister@...il.com>,
        Tristram Ha <Tristram.Ha@...rochip.com>,
        Woojung Huh <woojung.huh@...rochip.com>
Subject: Re: [PATCH 1/2] net: phy: micrel: Discern KSZ8051 and KSZ8795 PHYs

On 10.10.2019 21:12, Marek Vasut wrote:
> The KSZ8051 PHY and the KSZ8794/KSZ8795/KSZ8765 switch share exactly the
> same PHY ID. Since KSZ8051 is higher in the ksphy_driver[] list of PHYs
> in the micrel PHY driver, it is used even with the KSZ87xx switch. This
> is wrong, since the KSZ8051 configures registers of the PHY which are
> not present on the simplified KSZ87xx switch PHYs and misconfigures
> other registers of the KSZ87xx switch PHYs.
> 
> Fortunatelly, it is possible to tell apart the KSZ8051 PHY from the
> KSZ87xx switch by checking the Basic Status register Bit 0, which is
> read-only and indicates presence of the Extended Capability Registers.
> The KSZ8051 PHY has those registers while the KSZ87xx switch does not.
> 
> This patch implements simple check for the presence of this bit for
> both the KSZ8051 PHY and KSZ87xx switch, to let both use the correct
> PHY driver instance.
> 
> Signed-off-by: Marek Vasut <marex@...x.de>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Florian Fainelli <f.fainelli@...il.com>
> Cc: George McCollister <george.mccollister@...il.com>
> Cc: Heiner Kallweit <hkallweit1@...il.com>
> Cc: Tristram Ha <Tristram.Ha@...rochip.com>
> Cc: Woojung Huh <woojung.huh@...rochip.com>
> ---
> NOTE: It was also suggested to populate phydev->dev_flags to discern
>       the PHY from the switch, this does not work for setups where
>       the switch is used as a PHY without a DSA driver. Checking the
>       BMSR Bit 0 for Extended Capability Register works for both DSA
>       and non-DSA usecase.
> ---
>  drivers/net/phy/micrel.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> index 2fea5541c35a..54d483de024f 100644
> --- a/drivers/net/phy/micrel.c
> +++ b/drivers/net/phy/micrel.c
> @@ -341,6 +341,22 @@ static int ksz8041_config_aneg(struct phy_device *phydev)
>  	return genphy_config_aneg(phydev);
>  }
>  
> +static int ksz8051_match_phy_device(struct phy_device *phydev)
> +{
> +	int ret;
> +
> +	ret = phy_read(phydev, MII_BMSR);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* KSZ8051 PHY and KSZ8794/KSZ8795/KSZ8765 switch share the same
> +	 * exact PHY ID. However, they can be told apart by the extended
> +	 * capability registers presence. The KSZ8051 PHY has them while
> +	 * the switch does not.
> +	 */
> +	return ret & BMSR_ERCAP;

Idea and approach are right, but as-is could result in this driver
matching any (even non-Micrel) PHY devices with this bit set. You have
to check the PHY ID too. See Realtek PHY driver for an example.

> +}
> +
>  static int ksz8081_config_init(struct phy_device *phydev)
>  {
>  	/* KSZPHY_OMSO_FACTORY_TEST is set at de-assertion of the reset line
> @@ -364,6 +380,18 @@ static int ksz8061_config_init(struct phy_device *phydev)
>  	return kszphy_config_init(phydev);
>  }
>  
> +static int ksz8795_match_phy_device(struct phy_device *phydev)
> +{
> +	int ret;
> +
> +	ret = phy_read(phydev, MII_BMSR);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* See comment in ksz8051_match_phy_device() for details. */
> +	return !(ret & BMSR_ERCAP);
> +}
> +
>  static int ksz9021_load_values_from_of(struct phy_device *phydev,
>  				       const struct device_node *of_node,
>  				       u16 reg,
> @@ -1029,6 +1057,7 @@ static struct phy_driver ksphy_driver[] = {
>  	.get_sset_count = kszphy_get_sset_count,
>  	.get_strings	= kszphy_get_strings,
>  	.get_stats	= kszphy_get_stats,
> +	.match_phy_device = ksz8051_match_phy_device,

If callback match_phy_device is implemented, then you can remove
phy_id and phy_id_mask. Check phy_bus_match().

>  	.suspend	= genphy_suspend,
>  	.resume		= genphy_resume,
>  }, {
> @@ -1148,6 +1177,7 @@ static struct phy_driver ksphy_driver[] = {
>  	.config_init	= kszphy_config_init,
>  	.config_aneg	= ksz8873mll_config_aneg,
>  	.read_status	= ksz8873mll_read_status,
> +	.match_phy_device = ksz8795_match_phy_device,
>  	.suspend	= genphy_suspend,
>  	.resume		= genphy_resume,
>  }, {
> 

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