On 28/04/17 14:22, Andrew Lunn wrote:
Since you are using DSA, you will have DSA tags enabled on frames
to/from the switch. This adds an extra 8 byte header in the frame. My
guess is, it is this header, not the VLAN tag which is causing you MTU
issues.
But it is strange because, as I have said above, we have the same
configuration working properly on a kernel 4.1 (with OpenWrt), and
we have the MTU set to 1500.
Hi Andrew,
Sorry for the delay in my answer, I was out of the office.
If you look at sky2.c:
static unsigned sky2_get_rx_threshold(struct sky2_port *sky2)
{
unsigned size;
/* Space needed for frame data + headers rounded up */
size = roundup(sky2->netdev->mtu + ETH_HLEN + VLAN_HLEN, 8);
/* Stopping point for hardware truncation */
return (size - 8) / sizeof(u32);
}
This is not going to be big enough for a frame with a DSA header.
Then, would be a good fix add 8 bytes to the size variable in this function?
I think this is the first time i've seen sky2 used in a DSA
setup. mv643xx or mvneta is generally what is used, when using Marvell
chipsets. These drivers are more lenient about MTU, and are happy to
pass frames with additional headers.
We use the mv88e6xxx (as our switch is mv88e6176) and it depends on
DSA driver in the kernel (isn't it?).
That is correct. But i was talking about the Ethernet interface. All
the designs i've seen use an mv643xxx Ethernet interface, or an mvneta
interface. This is the first time i've seen a sky2 used, which is why
i'm not too surprised you have issues.
Changing the MTU like this is not a good fix. It will allow you to
receive frames which are bigger, but it also means the local network
stack will generate bigger frames to be transmitted. You probably need
to modify the sky2 driver to allow it to receive frames bigger than
the interface MTU, by about 8 bytes.
Should the DSA driver remove the DSA tags before pass the frames to
sky2 interface?
The DSA driver is adding the DSA tags to the frame and passing these
tagged frames to the sky2 interface. Frames going to/from the switch
will always have such tags.
[ 4901.032989] sky2 0000:04:00.0 marvell: tx timeout
[ 4904.722670] sky2 0000:04:00.0 marvell: Link is up at 1000 Mbps,
full duplex, flow control both
Between the sky2 and the switch, do you have two back-to-back PHYs or
are you connecting the RGMII interfaces together?
I think that we have two back-to-back PHYs, but I am going to double
check this with the hardware team.
This could be your problem them. The mv88e6xxx switch driver assumes
there is a straight rgmii-rgmii connection, no PHYs. So it hard
configures the 'CPU' port to its fastest speed, with the link forced
up. If you actually have a PHY there, this might not work so well. I
don't know if the switch PHY is going to do autoneg correctly. Try
using ethtool to look at the sky2 PHY and see what state it is in.
Andrew
The output of ethtool of sky2 interface is the following:
Settings for marvell:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: No
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
MDI-X: Unknown
Supports Wake-on: pg
Wake-on: d
Current message level: 0x000000ff (255)
drv probe link timer ifdown ifup rx_err
tx_err
Link detected: yes
And the output of ethtool of eth2@marvell (interface that I have connected):
Settings for eth2:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Link partner advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Link partner advertised pause frame use: No
Link partner advertised auto-negotiation: No
Speed: 100Mb/s
Duplex: Full
Port: MII
PHYAD: 2
Transceiver: external
Auto-negotiation: on
Supports Wake-on: d
Wake-on: d
Link detected: yes
Do you see something strange in these outputs?
Thanks,
Rafa
