Re: [PATCH] r8169: Load MAC address from device tree if present

Heiner Kallweit
2019-01-25T19:23:41Z

On 25.01.2019 20:07, Andrew Lunn wrote:
>> Andrew, for my understanding: What do you think is wrong with the
>> alignment requirement? It was introduced because we do a 32 bit access
>> to the start address of the array and want to avoid an unaligned access.
>
> Hi Heiner
>
> Because you are doing pointer aliasing, the compiler will by default
> generate bad code, doing unaligned access. Adding the attribute works
> around this. But it is just a work around. Since this is very slow
> path code, i would just avoid the pointer aliasing, write a bit more C
> code as Thierry suggested, and the optimiser will probably figure out
> what is going on and produce reasonable code.
>
> Also, in general, by avoiding pointer aliasing, you allow static code
> checkers to work better. They are more likely to discover buffer
> overruns, etc.
>
> Andrew
>

Thanks, good to know.

The following doesn't hurt us here, but things like this have to be
considered too. According to chip spec:

"The ID registers 0-5 are only permitted to write by 4-byte access.
Read access can be byte, word, or double word access."

Heiner