Re: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

On Fri, Nov 30 2018, Bjørn Mork wrote:

gerg@kernel.org writes:

quoted

I have been working towards supporting the MT7530 switch as used in the
MediaTek MT7621 SoC. Unlike the MediaTek MT7623 the MT7621 is built around
a dual core MIPS CPU architecture. But underneath it is what appears to
be the same 7530 switch.

Great!  Good to see someone pushing this idea forward.

quoted

The following 3 patches are more of an RFC than anything. They allow
use of the mt7530 dsa driver on this device - though with some issues
still to resolve. The primary change required is to not use the 7623
specific clock and regulator setup - none of that applies when using
the 7621 (and maybe other devices?). The other change required is to
set the 7530 MFC register CPU port number and enable bit.

The unresolved issues I still have appear to be more related to the
MT7621 ethernet driver (drivers/staging/mt7621-eth/*). I am hoping
someone might have some ideas on these. I don't really have any good
documentation on the ethernet devices on the 7621, so I am kind of
working in the dark here.

No offense, but the mt7621-eth driver in staging is horrible.  What both
René and I have had some success with is adapting the mtk_eth_soc driver
already in drivers/net/ethernet/mediatek/.  Yes, I know this is supposed
to be for other SoCs, but the basic design is obviously the same.

I have had some success with a first hackish attemt based on OpenWrt.
You can find the early tree here, but note that my focus was basically
getting one specific MT7621 board up and running:
https://github.com/bmork/LEDE/tree/mt7621-with-mainline-eth-driver

This patch has most of the necessary changes to enable that driver for
MT7621:
https://github.com/bmork/LEDE/commit/3293bc63f5461ca1eb0bbc4ed90145335e7e3404

Not a big deal, as you can see.  There is of course a reason I didn't
submit this here yet: It is by no means finished...  But it works. And I
have both GMACs working with this driver, which was my primary goal.

Thanks a lot for posting this.  I'd be very happy to see the staging
driver disappear once this is ready and in mainline.

I got your patch working on 4.20-rc5 and did a performance comparison.
With the staging driver (using iperf3) I get
  220 MBit/sec in
  680 MBit/sec out

with the patched mainline driver I get
  190 MBit/sec in
   93 MBit/sec out

(numbers are a bit rubbery, but within 10%)

I haven't looked into why this might be, but thought I would mention it.

Strangely when I test with scp, I get about 10MB/sec in both directions
with both drivers.  Maybe the CPU limits encryption speed.

I have a 4.4-based kernel where I get 940MBit/sec both ways - using a
precursor of the current staging driver.

Thanks,
NeilBrown

quoted

1. TX packets are not getting an IP header checksum via the normal
   off-loaded checksumming when in DSA mode. I have to switch off
   NETIF_F_IP_CSUM, so the software stack generates the checksum.
   That checksum offloading works ok when not using the 7530 DSA driver.

Hmm.  How do I test this?

quoted

2. Maximal sized RX packets get silently dropped. So receive side packets
   that are large (perfect case is the all-but-last packets in a fragemented
   larger packet) appear to be dropped at the mt7621 ethernet MAC level.
   The 7530 MIB switch register counters show receive packets at the physical
   switch port side and at the CPU switch port - but I get no packets
   received or errors in the 7621 ethernet MAC. If I set the mtu of the
   server at the other end a little smaller (a few bytes is enough) then
   I get all the packets through. It seems like the DSA/VLAN tag bytes
   are causing a too large packet to get silently dropped somewhere.

Are you referring to the configured MTU size or some other maximal size?
If MTU, then I don't seem to have this issue with the driver from
drivers/net/ethernet/mediatek/.



Bjørn