netdev - Re: [PATCH net-next] net: phy: let genphy_c45_read

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Date:   Thu, 7 Feb 2019 23:06:32 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        Russell King <linux@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: let genphy_c45_read_link manage the
 devices to check

On 07.02.2019 22:54, Heiner Kallweit wrote:
> On 07.02.2019 21:50, Andrew Lunn wrote:
>>> Thanks, Andrew. Right, the Aquantia PHY doesn't seem to have the C22EXT
>>> MMD. Because the Aquantia PHY has no device 29 in its package the code
>>> should work.
>>
>> It lists device 29 in its devices in package. So the current code does
>> look there.
>>
> I just looked for a description of a device 29. Strange that the device
> list states it's there and then it's not there.
> 
> When checking that I was scratching my head because of the following code
> in genphy_c45_read_link:
> 
> devad = __ffs(mmd_mask);
> mmd_mask &= ~BIT(devad);
> 
> AFAIK __ffs() returns the posix bit number, means it returns 1 for bit 0.
> Then this code piece seems to be wrong because I think the intention is
> to clear the bit we just found. Instead we clear the next bit.
> 
Nope, it doesn't seem to be the posix version .. Just checked the code of __ffs().

> And device 0 isn't really a device but a flag "Clause 22 registers present".
> So far we may have been lucky because to supported 10G PHY has this flag set.
> But if this flag is set and we try to access a register 0.1 then we may be
> in trouble again. Therefore I think we need to exclude also device 0.
> Or do I miss something?
> 
>>> So it seems we have to exclude device C22EXT in general. I'll add that
>>> and submit a v2.
>>
>> Yes.
>>
>> 	Andrew
>>
> Heiner
>