netdev - RE: [PATCH net-next] net: fec: Allow reception of frames bigger than 1522 bytes

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Date:   Mon, 31 Jul 2017 01:41:01 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>
CC:     netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] net: fec: Allow reception of frames bigger than
 1522 bytes

From: Andrew Lunn <andrew@...n.ch> Sent: Monday, July 31, 2017 1:36 AM
>The FEC Receive Control Register has a 14 bit field indicating the longest frame
>that my be received. It is being set to 1522. Frames longer than this are

My -> may

>discarded, but counted as being in error.
>
>When using DSA, frames from the switch has an additional header, either 4 or
>8 bytes if a Marvell switch is used. Thus a full MTU frame of 1522 bytes
>received by the switch on a port becomes 1530 bytes when passed to the host
>via the FEC interface.
>
>Change the maximum receive size to 2048 - 64, where 64 is the maximum
>rx_alignment applied on the receive buffer for AVB capable FEC cores. Use this
>value also for the maximum receive buffer size. The driver is already allocating
>a receive SKB of 2048 bytes, so this change should not have any significant
>effects.
>
>Tested on imx51, imx6, vf610.
>
>Signed-off-by: Andrew Lunn <andrew@...n.ch>
>---
> drivers/net/ethernet/freescale/fec_main.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/net/ethernet/freescale/fec_main.c
>b/drivers/net/ethernet/freescale/fec_main.c
>index a6e323f15637..47ee74a17a9f 100644
>--- a/drivers/net/ethernet/freescale/fec_main.c
>+++ b/drivers/net/ethernet/freescale/fec_main.c
>@@ -173,10 +173,12 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet
>MAC address");  #endif /* CONFIG_M5272 */
>
> /* The FEC stores dest/src/type/vlan, data, and checksum for receive packets.
>+ *
>+ * 2048 byte skbufs are allocated. However, alignment requirements
>+ * varies between FEC variants. Worst case is 64, so round down by 64.
>  */
>-#define PKT_MAXBUF_SIZE		1522
>+#define PKT_MAXBUF_SIZE		(round_down(2048 - 64, 64))
> #define PKT_MINBUF_SIZE		64
>-#define PKT_MAXBLR_SIZE		1536
>
> /* FEC receive acceleration */
> #define FEC_RACC_IPDIS		(1 << 1)
>@@ -851,7 +853,7 @@ static void fec_enet_enable_ring(struct net_device
>*ndev)
> 	for (i = 0; i < fep->num_rx_queues; i++) {
> 		rxq = fep->rx_queue[i];
> 		writel(rxq->bd.dma, fep->hwp + FEC_R_DES_START(i));
>-		writel(PKT_MAXBLR_SIZE, fep->hwp + FEC_R_BUFF_SIZE(i));
>+		writel(PKT_MAXBUF_SIZE, fep->hwp + FEC_R_BUFF_SIZE(i));
>
> 		/* enable DMA1/2 */
> 		if (i)
>--
>2.13.2