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

[Karumanchi, Vineeth]

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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