Patch for arch/ppc/8xx_io/fec.c

[Jean-Denis Boyer]

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Hello.

I've attached to this mail a patch for the FEC driver
on the Motorola MPC8xx embedded CPU.

This patch includes both a bug fix, and a new PHYter implementation.

 Symptom
---------
I was experiencing problems of "transmission timeout" when heavily
loading the network (throughput tests), particularly when the board
was wired to a 10MBits link (but I could also reproduce it on 100Mbits
using the packet sockets). The user process was then "held" by the IP
stack, I had no choice but to kill it.

 Bug description
-----------------
When, in rare cases, the ring buffer became full, the driver was =
stopping
the network queue, which is OK. But, it did not set a flag to restart
the queue in the transmission interrupt service routine.

 Bug fix
---------
I only had to set this flag, at the same time the network queue was =
stopped
(already wrapped in a spin lock).

Supplement:
 PHYter implementation
-----------------------
My board uses the NS chip model DP83843BVJE, for which I filled out the
needed structures.
However, I could not test the PHYter interrupt since it is not wired to =
the
PPC on our board
(but it is enabled in this patch). I had to code a polling routine (not
included in this patch).

It might be a good idea to move all these implementations outside of
"fec.c".
It might be also useful to choose the supported models through the =
kernel
configuration.
Perhaps I will work on that during the next weeks...

By the way, who is maintaining that part (MPC8xx, MPC82xx) of the =
kernel?

 Other issue=20
-------------
I have another problem I will have to address. I'm experiencing a =
strange
behaviour
in the response time when I 'ping flood' my board.

Through the 10Mbits, everything works fine, the average response time =
is
468us,
with realist minimum and maximum values.

  > round-trip min/avg/max/mdev =3D 0.458/0.468/0.600/0.029 ms

But, through the 100Mbits, the response time ranges from 0.26ms to =
10ms,
and an average of about 5ms, always different from test to test.

  > round-trip min/avg/max/mdev =3D 0.265/6.764/10.311/4.512 ms

Strangely, the board is not running anything but bash.
If a start 'top' with a refresh period of 1 second, I get a lower =
average,
but still the same min and max.

  > round-trip min/avg/max/mdev =3D 0.264/0.583/10.018/1.421 ms

If I start an NFS copy of a big file, the maximum gets down to 2ms.

The maximum of 10ms sounds like the timer tick.
Since it is working well in 10Mbps and not in 100Mbps,
can I suspect a problem with the Ethernet driver?

Thank you for your time.

--------------------------------------------
 Jean-Denis Boyer, B.Eng., Technical Leader
 Mediatrix Telecom Inc.
 4229 Garlock Street
 Sherbrooke (Qu=E9bec)
 J1L 2C8  CANADA
--------------------------------------------

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