Re: [PATCH net-next] tg3: normalize inherited M3000 register byte order

[Andrew Lunn]

On Fri, Oct 09, 2026 at 02:52:57PM +0200, Magnus Lindholm wrote:
> Hi Andrew,
> 
> On Fri, Oct 9, 2026 at 2:09 PM Andrew Lunn <andrew@xxxxxxx> wrote:
> >
> > > > Is there a legitimate reason you would want the bytes are swapped?
> >
> > You missed answering this. I'm guessing, but does the hardware offer
> > this to make big endian machines more efficient?
> >
> > Please could you look at the driver and think about what would happen
> > on a big endian machine. Is the change still correct?
> >
> >         Andrew
> 
> You're right, my earlier reply missed the underlying question.
> 
> That is a plausible reason for providing the hardware swap mode:
> it can accommodate big-endian accesses without software byte
> swapping. I haven't verified Broadcom's design rationale.
> 
> However, Linux tg3 already initializes misc_host_ctrl with WORD_SWAP set
> and BYTE_SWAP clear on both little- and big-endian builds, before
> this helper runs.
> 
> The helper restores that existing setting. Its swab32() compensates
> for the device's inherited register state, not CPU endianness.
> Subsequent accesses use the normal driver path, and the separate
> __BIG_ENDIAN handling for DMA remains unchanged.
> 
> That is why I believe the correction is appropriate on either
> endianness. The runtime tests were on the M3000 running big-endian
> SPARC64.

Please expand the commit message to show you have thought about this.

       Andrew