Patch "net: fec: Allow reception of frames bigger than 1522 bytes" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

net: fec: Allow reception of frames bigger than 1522 bytes

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-fec-allow-reception-of-frames-bigger-than-1522-bytes.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrew Lunn <[email protected]>
Date: Sun, 30 Jul 2017 19:36:05 +0200
Subject: net: fec: Allow reception of frames bigger than 1522 bytes

From: Andrew Lunn <[email protected]>

[ Upstream commit fbbeefdd21049fcf9437c809da3828b210577f36 ]

The FEC Receive Control Register has a 14 bit field indicating the longest frame that may be received. It is being set to 1522. Frames longer than this are 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.

---
 drivers/net/ethernet/freescale/fec_main.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -172,10 +172,12 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet
 #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)

@@ -853,7 +855,7 @@ static void fec_enet_enable_ring(struct
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net-igmp-use-correct-source-address-on-igmpv3-reports.patch queue-4.9/net-mvmdio-disable-unprepare-clocks-in-eprobe_defer-case.patch queue-4.9/net-fec-allow-reception-of-frames-bigger-than-1522-bytes.patch