netdev - RE: [PATCH net] net/mlx4_en: correct the endianness of doorbell

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CA04A51@AcuExch.aculab.com>
Date:	Mon, 8 Dec 2014 10:00:19 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Eric Dumazet' <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	"weiyang@...ux.vnet.ibm.com" <weiyang@...ux.vnet.ibm.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gideonn@...lanox.com" <gideonn@...lanox.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"amirv@...lanox.com" <amirv@...lanox.com>
Subject: RE: [PATCH net] net/mlx4_en: correct the endianness of doorbell_qpn
 on big endian platform

From: Eric Dumazet
> On Fri, 2014-12-05 at 21:31 -0800, David Miller wrote:
> 
> > Guys, let's figure out what we are doing with this patch.
> > --
> 
> Oh well, patch is fine, please apply it, thanks !

I'm not to sure that the patch doesn't generate a software byteswap
followed by a byteswapping write on ppc - clearly not ideal.
It might even generate back to back software byteswaps.

If the write to the doorbell register includes a byteswap on BE (ppc)
then there is no real value in keeping the value as BE.

OTOH ppc ought to have ways of doing IO writes without the byteswap
(and byteswapping accesses to non-io memory for that matter).

What happens on a BE system with BE peripherals is another matter.

	David