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

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Message-ID: <20190207221914.7ckuso5rqraufasv@shell.armlinux.org.uk>
Date:   Thu, 7 Feb 2019 22:19:14 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "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 Thu, Feb 07, 2019 at 10:54:51PM +0100, 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.

I think you're wrong.  Look at include/asm-generic/bitops/__ffs.h.  If
'word' is 0x00000001, then the function returns zero.  If 'word' is
0x00000002, it returns 1, etc.

-- 
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