Patch "net: lan966x: Fix FDMA when MTU is changed" has been added to the 6.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    net: lan966x: Fix FDMA when MTU is changed

to the 6.0-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-lan966x-fix-fdma-when-mtu-is-changed.patch
and it can be found in the queue-6.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 42e88d53d65f698a00175c5f02166900713aa704
Author: Horatiu Vultur <horatiu.vultur@xxxxxxxxxxxxx>
Date:   Sun Oct 30 22:36:36 2022 +0100

    net: lan966x: Fix FDMA when MTU is changed
    
    [ Upstream commit 872ad758f9b7fb4eb42aebaf64e50c5b29b7ffe5 ]
    
    When MTU is changed, FDMA is required to calculate what is the maximum
    size of the frame that it can received. So it can calculate what is the
    page order needed to allocate for the received frames.
    The first problem was that, when the max MTU was calculated it was
    reading the value from dev and not from HW, so in this way it was
    missing L2 header + the FCS.
    The other problem was that once the skb is created using
    __build_skb_around, it would reserve some space for skb_shared_info.
    So if we received a frame which size is at the limit of the page order
    then the creating will failed because it would not have space to put all
    the data.
    
    Fixes: 2ea1cbac267e ("net: lan966x: Update FDMA to change MTU.")
    Signed-off-by: Horatiu Vultur <horatiu.vultur@xxxxxxxxxxxxx>
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index 69f741db25b1..407a6c125515 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -668,12 +668,14 @@ static int lan966x_fdma_get_max_mtu(struct lan966x *lan966x)
 	int i;
 
 	for (i = 0; i < lan966x->num_phys_ports; ++i) {
+		struct lan966x_port *port;
 		int mtu;
 
-		if (!lan966x->ports[i])
+		port = lan966x->ports[i];
+		if (!port)
 			continue;
 
-		mtu = lan966x->ports[i]->dev->mtu;
+		mtu = lan_rd(lan966x, DEV_MAC_MAXLEN_CFG(port->chip_port));
 		if (mtu > max_mtu)
 			max_mtu = mtu;
 	}
@@ -733,6 +735,8 @@ int lan966x_fdma_change_mtu(struct lan966x *lan966x)
 
 	max_mtu = lan966x_fdma_get_max_mtu(lan966x);
 	max_mtu += IFH_LEN * sizeof(u32);
+	max_mtu += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	max_mtu += VLAN_HLEN * 2;
 
 	if (round_up(max_mtu, PAGE_SIZE) / PAGE_SIZE - 1 ==
 	    lan966x->rx.page_order)
diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
index 989e5f045d7e..4a3cb7579420 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
@@ -394,7 +394,7 @@ static int lan966x_port_change_mtu(struct net_device *dev, int new_mtu)
 
 	err = lan966x_fdma_change_mtu(lan966x);
 	if (err) {
-		lan_wr(DEV_MAC_MAXLEN_CFG_MAX_LEN_SET(old_mtu),
+		lan_wr(DEV_MAC_MAXLEN_CFG_MAX_LEN_SET(LAN966X_HW_MTU(old_mtu)),
 		       lan966x, DEV_MAC_MAXLEN_CFG(port->chip_port));
 		dev->mtu = old_mtu;
 	}