netdev - Re: [PATCH net-next] net: enetc: use get/put_unaligned() for mac address handling

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Date:   Fri, 04 Jun 2021 15:27:48 +0200
From:   Michael Walle <michael@...le.cc>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Claudiu Manoil <claudiu.manoil@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next] net: enetc: use get/put_unaligned() for mac
 address handling

Am 2021-06-04 14:44, schrieb Heiner Kallweit:
> On 04.06.2021 14:30, Michael Walle wrote:
>> The supplied buffer for the MAC address might not be aligned. Thus
>> doing a 32bit (or 16bit) access could be on an unaligned address. For
>> now, enetc is only used on aarch64 which can do unaligned accesses, 
>> thus
>> there is no error. In any case, be correct and use the 
>> get/put_unaligned()
>> helpers.
>> 
>> Signed-off-by: Michael Walle <michael@...le.cc>
>> ---
>>  drivers/net/ethernet/freescale/enetc/enetc_pf.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/net/ethernet/freescale/enetc/enetc_pf.c 
>> b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
>> index 31274325159a..a96d2acb5e11 100644
>> --- a/drivers/net/ethernet/freescale/enetc/enetc_pf.c
>> +++ b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
>> @@ -1,6 +1,7 @@
>>  // SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
>>  /* Copyright 2017-2019 NXP */
>> 
>> +#include <asm/unaligned.h>
>>  #include <linux/mdio.h>
>>  #include <linux/module.h>
>>  #include <linux/fsl/enetc_mdio.h>
>> @@ -17,15 +18,15 @@ static void enetc_pf_get_primary_mac_addr(struct 
>> enetc_hw *hw, int si, u8 *addr)
>>  	u32 upper = __raw_readl(hw->port + ENETC_PSIPMAR0(si));
>>  	u16 lower = __raw_readw(hw->port + ENETC_PSIPMAR1(si));
>> 
>> -	*(u32 *)addr = upper;
>> -	*(u16 *)(addr + 4) = lower;
>> +	put_unaligned(upper, (u32 *)addr);
>> +	put_unaligned(lower, (u16 *)(addr + 4));
> 
> I think you want to write little endian, therefore on a BE platform
> this code may be wrong. Better use put_unaligned_le32?
> By using these versions of the unaligned helpers you could also
> remove the pointer cast.

I wasn't sure about the endianness. Might be the case, that on BE
platforms, the endianess of the register will swap too. (OTOH I
could use aarch64 with BE..)

But I'm fine with changing it. I'd presume this being the only
platform for now it doesn't really matter.

-michael