[U-Boot] [PATCH 2/4] net: tweak eth_device layout to simplify enetaddr use

[Mike Frysinger]

On Friday 11 November 2011 06:55:45 Wolfgang Denk wrote:
> Mike Frysinger wrote:
> > The current eth_device leaves a 2 byte hole after "enetaddr" and before
> > "iobase".  Since the enetaddr member has to be 6 bytes, we might as well
> > fill that 2 byte hole with something useful.
> > 
> > Further, most device drivers want to load enetaddr from memory into the
> > hardware as 1 32bit value and 1 16bit value.
> > 
> > So re-arrange the structure slightly, and add an anonymous union to make
> > 
> > eth_device even better:
> >  - expand the name field to fill the 2 byte hole
> >  - make sure enetaddr is aligned, and provides 32bit/16bit members
> 
> I'm OK with expanding the name[] field, but as Thomas pointed out,
> providing "convenient" u32 / u16 variables for the MAC address is
> actually a faux ami that misleads people into using these variables
> without thinking about endianess and such.
> 
> Please omit this part.

there's always the endian issue.  i'd wager that the vast majority of the 
time, the endian of the target hardware is the same as the core.  so omitting 
this for odd devices or device driver writers who aren't careful is being too 
pessimistic imo.  i can add qualifiers to the name like "enetaddr_cpu32" if you 
want.  looking at the generated code shows really nice improvements: a single 
cpu load instead of 4 loads interspersed with bitshifts.
-mike
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part.
Url : http://lists.denx.de/pipermail/u-boot/attachments/20111111/0821e42c/attachment.pgp