Hi Vineeth,
On Thu, Jun 20, 2024 at 09:29:01PM +0530, Karumanchi, Vineeth wrote:
> 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:
...
> > > @@ -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 for your response, your proposal looks good to me.
