linux-kernel - Re: [PATCH net-next v6 3/4] net: macb: Add ARP support to WOL

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Message-ID: <616a10c5-9c72-4221-a181-6251e808b9b8@amd.com>
Date: Thu, 20 Jun 2024 21:29:01 +0530
From: "Karumanchi, Vineeth" <vineeth.karumanchi@....com>
To: Simon Horman <horms@...nel.org>
Cc: nicolas.ferre@...rochip.com, claudiu.beznea@...on.dev,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
 conor+dt@...nel.org, linux@...linux.org.uk, vadim.fedorenko@...ux.dev,
 andrew@...n.ch, netdev@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, git@....com
Subject: Re: [PATCH net-next v6 3/4] net: macb: Add ARP support to WOL

Hi Simon,

On 6/18/2024 4:26 PM, Simon Horman wrote:
> On Mon, Jun 17, 2024 at 12:34:12PM +0530, Vineeth Karumanchi wrote:
>> Extend wake-on LAN support with an ARP packet.

...

> ...
> 
>> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> 
> ...
> 
>> @@ -84,8 +85,7 @@ struct sifive_fu540_macb_mgmt {
>>   #define GEM_MTU_MIN_SIZE	ETH_MIN_MTU
>>   #define MACB_NETIF_LSO		NETIF_F_TSO
>>   
>> -#define MACB_WOL_HAS_MAGIC_PACKET	(0x1 << 0)
>> -#define MACB_WOL_ENABLED		(0x1 << 1)
>> +#define MACB_WOL_ENABLED		(0x1 << 0)
> 
> 
> nit: BIT() could be used here
> 

OK.

>>   
>>   #define HS_SPEED_10000M			4
>>   #define MACB_SERDES_RATE_10G		1
> 
> ...
> 
>> @@ -5290,6 +5289,14 @@ static int __maybe_unused macb_suspend(struct device *dev)
>>   		macb_writel(bp, TSR, -1);
>>   		macb_writel(bp, RSR, -1);
>>   
>> +		tmp = (bp->wolopts & WAKE_MAGIC) ? MACB_BIT(MAG) : 0;
>> +		if (bp->wolopts & WAKE_ARP) {
>> +			tmp |= MACB_BIT(ARP);
>> +			/* write IP address into register */
>> +			tmp |= MACB_BFEXT(IP,
>> +					 (__force u32)(cpu_to_be32p((uint32_t *)&ifa->ifa_local)));
> 
> Hi Vineeth and Harini,
> 
> I guess I must be reading this wrong, beause I am confused
> by the intent of the endeness handling above.
> 
> * ifa->ifa_local is a 32-bit big-endian value
> 
> * It's address is cast to a 32-bit host-endian pointer
> 
>    nit: I think u32 would be preferable to uint32_t; this is kernel code.
> 
> * The value at this address is then converted to a host byte order value.
> 
>    nit: Why is cpu_to_be32p() used here instead of the more commonly used
>         cpu_to_be32() ?
> 
>    More importantly, why is a host byte order value being converted from
>    big-endian to host byte order?
> 
> * The value returned by cpu_to_be32p, which is big-endian, because
>    that is what that function does, is then cast to host-byte order.
> 
> 
> So overall we have:
> 
> 1. Cast from big endian to host byte order
> 2. Conversion from host byte order to big endian
>     (a bytes-swap on litte endian hosts; no-op on big endian hosts)
> 3. Cast from big endian to host byte oder
> 
> All three of these steps seem to warrant explanation.
> And the combination is confusing to say the least.
> 

tmp |= MACB_BFEXT(IP, be32_to_cpu(ifa->ifa_local));

The above snippet will address above points.
Consider the ip address is : 11.11.70.78

1. ifa->ifa_local : returns be32 -> 0x4E460b0b
2. be32_to_cpu(ifa->ifa_local) : converts be32 to host byte order u32: 
0x0b0b464e

There are no sparse errors as well.
I will make the change, please let me know your suggestions/thoughts.

Thanks
🙏 vineeth

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