netdev - RE: [Patch net-next 08/11] net:fec: change FEC alignment to 64 bytes for ARM platform

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D17487196@AcuExch.aculab.com>
Date:	Thu, 4 Sep 2014 08:50:40 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Frank Li' <Frank.Li@...escale.com>,
	"b38611@...escale.com" <b38611@...escale.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"lznuaa@...il.com" <lznuaa@...il.com>
CC:	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Fugang Duan <B38611@...escale.com>
Subject: RE: [Patch net-next 08/11] net:fec: change FEC alignment to 64
 bytes for ARM platform

From: Frank Li
> From: Fugang Duan <B38611@...escale.com>
> 
> Since enet-avb has 64 bytes alignment limitation for rx DMA transfer.
> The previous enet IP for ARM platform has 16 bytes alignment for tx
> DMA transfer.

Do you mean rx or tx here? or both??

And can we beat up the hardware designers to stop these restrictions
on rx (in particular) ethernet buffer alignments?
A device isn't suitable for ethernet unless is can write the destination
mac address to a 4n+2 boundary.

	David

> 64 is the an integral number of 16, so change alignment
> to 64 bytes for all ARM platform, which don't impact the performance
> of previous platform.
> 
> Signed-off-by: Fugang Duan <B38611@...escale.com>
> Signed-off-by: Frank Li <Frank.Li@...escale.com>
> ---
>  drivers/net/ethernet/freescale/fec_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index a232245..b388e29f 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -65,7 +65,7 @@
>  static void set_multicast_list(struct net_device *ndev);
> 
>  #if defined(CONFIG_ARM)
> -#define FEC_ALIGNMENT	0xf
> +#define FEC_ALIGNMENT	0x3f
>  #else
>  #define FEC_ALIGNMENT	0x3
>  #endif
> --
> 1.9.1
> 
> --
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