netdev - Re: [PATCH repost net-next] dsa: mv88e6xxx: Optimise atu

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Message-Id: <20170104.162718.86114638722981428.davem@davemloft.net>
Date:   Wed, 04 Jan 2017 16:27:18 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     andrew@...n.ch
Cc:     volodymyr.bendiuga@...il.com, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH repost net-next] dsa: mv88e6xxx: Optimise atu_get

From: Andrew Lunn <andrew@...n.ch>
Date: Wed, 4 Jan 2017 22:19:57 +0100

> On Wed, Jan 04, 2017 at 04:11:03PM -0500, David Miller wrote:
>> From: Andrew Lunn <andrew@...n.ch>
>> Date: Wed,  4 Jan 2017 19:56:24 +0100
>> 
>> > +static inline u64 ether_addr_to_u64(const u8 *addr)
>> > +{
>> > +	u64 u = 0;
>> > +	int i;
>> > +
>> > +	for (i = 0; i < ETH_ALEN; i++)
>> > +		u = u << 8 | addr[i];
>> > +
>> > +	return u;
>> > +}
>>  ...
>> > +static inline void u64_to_ether_addr(u64 u, u8 *addr)
>> > +{
>> > +	int i;
>> > +
>> > +	for (i = ETH_ALEN - 1; i >= 0; i--) {
>> > +		addr[i] = u & 0xff;
>> > +		u = u >> 8;
>> > +	}
>> > +}
>> 
>> I think these two routines behave differently on big vs little
>> endian.  And I doubt this was your intention.
> 
> I don't have a big endian system to test on.
> 
> I tried to avoid the usual pitfalls. I don't cast a collection of
> bytes to a u64, which i know has no chance of working. Accessing a MAC
> address as a byte array should be endian safe. The shift operation
> should also be endian safe.
> 
> What exactly do you think will behave differently?

Maybe I over-reacted.

I just ran some test programs in userspace on both little and big
endian and they checked out.

Sorry for the false alarm.

I'll apply this, thanks.