netdev - Re: [PATCH] net: phy: Fix c45 no phy detected logic

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Date:   Thu, 14 May 2020 21:59:07 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jeremy Linton <jeremy.linton@....com>, netdev@...r.kernel.org
Cc:     andrew@...n.ch, f.fainelli@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: Fix c45 no phy detected logic

On 14.05.2020 19:00, Jeremy Linton wrote:
> The commit "disregard Clause 22 registers present bit..." clears
> the low bit of the devices_in_package data which is being used
> in get_phy_c45_ids() to determine if a phy/register is responding
> correctly. That check is against 0x1FFFFFFF, but since the low
> bit is always cleared, the check can never be true. This leads to
> detecting c45 phy devices where none exist.
> 
> Lets fix this by also clearing the low bit in the mask to 0x1FFFFFFE.
> This allows us to continue to autoprobe standards compliant devices
> without also gaining a large number of bogus ones.
> 
> Fixes: 3b5e74e0afe3 ("net: phy: disregard "Clause 22 registers present" bit in get_phy_c45_devs_in_pkg")
> Cc: Heiner Kallweit <hkallweit1@...il.com>
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>  drivers/net/phy/phy_device.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index ac2784192472..b93d984d35cc 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -723,7 +723,7 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>  		if (phy_reg < 0)
>  			return -EIO;
>  
> -		if ((*devs & 0x1fffffff) == 0x1fffffff) {
> +		if ((*devs & 0x1ffffffe) == 0x1ffffffe) {
>  			/*  If mostly Fs, there is no device there,

Looks good to me, it would just be good to extend the comment and explain
why we exclude bit 0 here.


>  			 *  then let's continue to probe more, as some
>  			 *  10G PHYs have zero Devices In package,
> @@ -733,7 +733,7 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>  			if (phy_reg < 0)
>  				return -EIO;
>  			/* no device there, let's get out of here */
> -			if ((*devs & 0x1fffffff) == 0x1fffffff) {
> +			if ((*devs & 0x1ffffffe) == 0x1ffffffe) {
>  				*phy_id = 0xffffffff;
>  				return 0;
>  			} else {
>