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Date:   Thu, 25 Aug 2022 11:46:48 +0200
From:   Michael Walle <michael@walle.cc>
To:     =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>
Cc:     linux-mtd@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        netdev@vger.kernel.org, Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Rob Herring <robh+dt@kernel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Shawn Guo <shawnguo@kernel.org>, Li Yang <leoyang.li@nxp.com>,
        Frank Rowand <frowand.list@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Ansuel Smith <ansuelsmth@gmail.com>,
        Andrew Lunn <andrew@lunn.ch>
Subject: Re: [PATCH 5/8] net: add helper eth_addr_add()
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 <20211228142549.1275412-6-michael@walle.cc>
 <0d9a0ce5-ab34-cf05-158e-e25fc5595b4d@gmail.com>
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Am 2022-01-25 11:24, schrieb Rafał Miłecki:
> On 28.12.2021 15:25, Michael Walle wrote:
>> Add a helper to add an offset to a ethernet address. This comes in 
>> handy
>> if you have a base ethernet address for multiple interfaces.
>> 
>> Signed-off-by: Michael Walle <michael@walle.cc>
>> ---
>>   include/linux/etherdevice.h | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>> 
>> diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
>> index 2ad71cc90b37..9d621dc85290 100644
>> --- a/include/linux/etherdevice.h
>> +++ b/include/linux/etherdevice.h
>> @@ -486,6 +486,20 @@ static inline void eth_addr_inc(u8 *addr)
>>   	u64_to_ether_addr(u, addr);
>>   }
>>   +/**
>> + * eth_addr_add() - Add (or subtract) and offset to/from the given 
>> MAC address.
>> + *
>> + * @offset: Offset to add.
>> + * @addr: Pointer to a six-byte array containing Ethernet address to 
>> increment.
>> + */
>> +static inline void eth_addr_add(u8 *addr, long offset)
>> +{
>> +	u64 u = ether_addr_to_u64(addr);
>> +
>> +	u += offset;
>> +	u64_to_ether_addr(u, addr);
>> +}
> 
> Please check eth_hw_addr_gen() which contains identical code +
> eth_hw_addr_set().
> 
> You should probably make eth_hw_addr_gen() use your new function as a
> helper.

You'd need to copy the mac address first because eth_addr_add()
modifies the mac address in place. I don't see that this is
improving anything.

-michael