netdev - RE: [PATCH] mlx4_en: fix transmit of packages when blue frame is enabled

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Date:	Mon, 10 Oct 2011 09:20:38 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
	"Eli Cohen" <eli@....mellanox.co.il>
Cc:	<netdev@...r.kernel.org>, "Eli Cohen" <eli@...lanox.co.il>,
	<linuxppc-dev@...ts.ozlabs.org>,
	"Thadeu Lima de Souza Cascardo" <cascardo@...ux.vnet.ibm.com>,
	"Yevgeny Petrilin" <yevgenyp@...lanox.co.il>
Subject: RE: [PATCH] mlx4_en: fix transmit of packages when blue frame is enabled

> Then, this statement:
> 
> *(u32 *) (&tx_desc->ctrl.vlan_tag) |= ring->doorbell_qpn;

...
> instead do ... :

> 	*(u32 *) (&tx_desc->ctrl.vlan_tag) |=
cpu_to_be32(ring->doorbell_qpn);
> 
> (Also get rid of that cast and define vlan_tag as a __be32 to start
> with).

Agreed, casts that change the type of memory - *(foo *)&xxx - are
generally bad news unless you are casting a generic 'buffer' to
a specific structure.
I've seen far to much code that ends up being depending on the
endianness and system word size.

For the above I'd actually suggest making 'doorbell_qpn' have the
correct endianness in order to avoid the (potential) swap every
time it is set.

You also need to treble-check the required endianness for the
'vlan_tag' in the tx descriptor. What would be needed is the
MAC PCI slave were on an x86 (LE) system.

	David

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