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

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Message-ID: <20141208144237.GB8382@richard>
Date:	Mon, 8 Dec 2014 22:42:37 +0800
From:	Wei Yang <weiyang@...ux.vnet.ibm.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"'Eric Dumazet'" <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	"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

On Mon, Dec 08, 2014 at 10:00:19AM +0000, David Laight wrote:
>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

Thanks for your comment.

How about use __raw_writel() to replace the iowrite32()? Looks this is better,
if so, I will make up another version for this.

>
>	David
>

-- 
Richard Yang
Help you, Help me

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