linux-kernel - Re: [PATCH] net: phy: allow scanning busses with missing phys

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Date:   Tue, 24 Apr 2018 09:37:09 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Allan Nielsen <Allan.Nielsen@...rosemi.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: allow scanning busses with missing phys



On 04/24/2018 09:09 AM, Alexandre Belloni wrote:
> Some MDIO busses will error out when trying to read a phy address with no
> phy present at that address. In that case, probing the bus will fail
> because __mdiobus_register() is scanning the bus for all possible phys
> addresses.
> 
> In case MII_PHYSID1 returns -EIO or -ENODEV, consider there is no phy at
> this address and set the phy ID to 0xffffffff which is then properly
> handled in get_phy_device().

Humm, why not have your MDIO bus implementation do the scanning itself
in a reset() callback, which happens before probing the bus, and based
on the results, set phy_mask accordingly such that only PHYs present are
populated?

My only concern with your change is that we are having a special
treatment for EIO and ENODEV, so we must make sure MDIO bus drivers are
all conforming to that.

> 
> Suggested-by: Andrew Lunn <andrew@...n.ch>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> ---
>  drivers/net/phy/phy_device.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index ac23322a32e1..9e4ba8e80a18 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -535,8 +535,17 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
>  
>  	/* Grab the bits from PHYIR1, and put them in the upper half */
>  	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
> -	if (phy_reg < 0)
> +	if (phy_reg < 0) {
> +		/* if there is no device, return without an error so scanning
> +		 * the bus works properly
> +		 */
> +		if (phy_reg == -EIO || phy_reg == -ENODEV) {
> +			*phy_id = 0xffffffff;
> +			return 0;
> +		}
> +
>  		return -EIO;
> +	}
>  
>  	*phy_id = (phy_reg & 0xffff) << 16;
>  
> 

-- 
Florian