Subject: Re: [PATCH 02/12] fs_enet: Add MPC5121 FEC support.

From: David Jander <[email-masked]>
Date: Mon, 11 May 2009 08:56:58 +0200

On Friday 08 May 2009 09:52:51 David Miller wrote:
> From: John Rigby <[email-masked]>
> Date: Thu, 7 May 2009 20:02:53 -0600
>
> > Also don't forget that the register map is the same on 512x, mx and
> > coldfire platforms but not on the other ppc platforms so if you want
> > to one binary to rule them all you will need to have an offest table
> > or some such.
>
> I would suggest using ->read_reg() ->write_reg() methods for abstracting
> this.  That's how we handle all of the different way ESP scsi chips
> have their registers wired up.
>
> I/O register reads take hundreds, if not thousands of CPU cycles so,
> relatively speaking, the indirection costs absolutely nothing.

I fear the memory-mapped I/O of the PowerPC SoC is *slightly* faster, so in 
terms of cycle count, this WILL matter, although depending on how much 
register-I/O the driver does, overall performance impact _may_ still be 
negligible. I suggest testing this (benchmarks) before and after the change.

Best regsards,

-- 
David Jander
Protonic Holland.