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

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Date:	Sun, 09 Oct 2011 09:19:45 +0200
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
Cc:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eli Cohen <eli@...lanox.co.il>,
	"eli@....mellanox.co.il" <eli@....mellanox.co.il>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] mlx4_en: fix transmit of packages when blue frame is
 enabled

On Tue, 2011-10-04 at 17:26 -0300, Thadeu Lima de Souza Cascardo wrote:

>         if (ring->bf_enabled && desc_size <= MAX_BF && !bounce &&
> !vlan_tag) {
>                 *(u32 *) (&tx_desc->ctrl.vlan_tag) |=
> ring->doorbell_qpn;

Could this have endianness problems ?

>                 op_own |= htonl((bf_index & 0xffff) << 8);

Probably better to use cpu_to_be/lexx() here. Also make sure your
descriptors are defined with the appropriate __beXX or __leXX types
so sparse can tell you when you get this wrong

>                 /* Ensure new descirptor hits memory
>                 * before setting ownership of this descriptor to HW */
>                 wmb();
>                 tx_desc->ctrl.owner_opcode = op_own;

>                 wmb();
> 
>                 mlx4_bf_copy(ring->bf.reg + ring->bf.offset, (unsigned
> long *) &tx_desc->ctrl,
>                      desc_size);

What does the above do ?

>                 wmb();
> 
>                 ring->bf.offset ^= ring->bf.buf_size;

Is this HW visible ? It's a bit odd, are you doing double bufferring and
trying to flip a bit ? If it's HW visible, is endian correct ?
 
        } else {
>                 /* Ensure new descirptor hits memory
>                 * before setting ownership of this descriptor to HW */
>                 wmb();
>                 tx_desc->ctrl.owner_opcode = op_own;
> -               wmb();
> -               writel(ring->doorbell_qpn, ring->bf.uar->map +
> MLX4_SEND_DOORBELL);
>         }
> 
> +       wmb();
> +       writel(ring->doorbell_qpn, ring->bf.uar->map +
> MLX4_SEND_DOORBELL);
> +
> ---

Cheers,
Ben.


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