[RFC PATCH] ixgbe: Consider xsk pool's frame size for MTU size

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

The driver has to a ensure that a network packet is not using more than
one page for its data if a XDP program is used.
This results in an upper limit of 1500 bytes. This can be increased a
little if the MTU was programmed to 1514..3072 bytes before loading the
XDP program. By setting this increased MTU size the driver will set the
__IXGBE_RX_3K_BUFFER flag which in turn will allow to use 3KiB as the
upper limit.
This looks like a hack and the upper limit is could increased further.
If the user configured a memory pool then PAGE_SIZE is used as BSIZEPKT
and RLPML is set to pool's memory size as is the card's maximum frame
size.
The result is that a MTU of 3520 bytes can be programmed and every
packet is stored a single page.

If a RX ring has a pool assigned use its size while comparing for the
maximal MTU size.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---

According to my traces incoming packets with a size 70 or 3520 bytes all
end up in one page.
There is currently only one ring/RX-queue. I'm not sure if it is
reasonable to assume to have one RX-queue with xsk_pool and one without.

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 21 +++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 2ac5b82676f3b..d250c20a941e9 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -6723,6 +6723,23 @@ static void ixgbe_free_all_rx_resources(struct ixgbe_adapter *adapter)
 			ixgbe_free_rx_resources(adapter->rx_ring[i]);
 }
 
+static int ixgbe_validate_frame_size(unsigned int frame_size,
+				     struct ixgbe_ring *ring)
+{
+	struct xsk_buff_pool *xsk_pool;
+	unsigned int buf_len;
+
+	xsk_pool = ring->xsk_pool;
+	if (xsk_pool)
+		buf_len = xsk_pool_get_rx_frame_size(xsk_pool);
+	else
+		buf_len = ixgbe_rx_bufsz(ring);
+
+	if (frame_size > buf_len)
+		return -EINVAL;
+	return 0;
+}
+
 /**
  * ixgbe_change_mtu - Change the Maximum Transfer Unit
  * @netdev: network interface device structure
@@ -6742,7 +6759,7 @@ static int ixgbe_change_mtu(struct net_device *netdev, int new_mtu)
 		for (i = 0; i < adapter->num_rx_queues; i++) {
 			struct ixgbe_ring *ring = adapter->rx_ring[i];
 
-			if (new_frame_size > ixgbe_rx_bufsz(ring)) {
+			if (ixgbe_validate_frame_size(new_frame_size, ring)) {
 				e_warn(probe, "Requested MTU size is not supported with XDP\n");
 				return -EINVAL;
 			}
@@ -10127,7 +10144,7 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
 		if (ring_is_rsc_enabled(ring))
 			return -EINVAL;
 
-		if (frame_size > ixgbe_rx_bufsz(ring))
+		if (ixgbe_validate_frame_size(frame_size, ring))
 			return -EINVAL;
 	}
 
-- 
2.32.0