Hi,
I am the maintainer of a MPC5200 port of eCos at Elektrobit.
I found a race-condition in the implementation of our MSCAN
CAN-driver and it seems your driver has the same problem
(I reviewed your code for reference reasons):
http://git.kernel.org/?p=linux/kernel/git/davem/net-next-2.6.git;a=blob_plain;f=drivers/net/can/mscan/mscan.c;hb=HEAD
I first contacted Wolfram Sang personally and he pointed me
to the right sources and to this mailing list.
Problem is:
MSCAN has three Tx-Buffers. But only one buffer-interface.
So to select one buffer you must use a buffer selection (cantbsel)
register.
Your driver implementation selects the buffer in the
mscan_start_xmit() function and then fills the buffer with
payload.
But in the ISR mscan_isr() the buffer is also selected
to maintain the tx-stats.
Race-condition occurs if mscan_isr() interrupts mscan_start_xmit()
after it selects a buffer by writing to the tbsel register.
After ISR returns mscan_start_xmit will continue to write payload
into the wrong buffer.
A second race condition occurs with the cantier register.
The documentation says its an interrupt-enable register.
But in-fact it is a sort of acknowledgement register which
is accessed in both ISR and xmit function with load-and-store
operations.
The fix in my eCos driver was to lock the ISR from occuring during
cantbsel and cantier register are accessed inside the transmit function.
If you need a reference-implementation I can send you my
implementation of the MSCAN driver for eCos operating system.
It differs with your implementation because it is able to
abort buffers whenever a Can-Message arrives at the Tx-API
with has higher priority than the messages currently in the
buffers (to avoid starvation on the bus).
Perhaps the following lines could be written simpler
in function mscan_isr():
cantier = in_8(®s->cantier) & MSCAN_TXE;
cantflg = in_8(®s->cantflg) & cantier;
if (cantier && cantflg) {
...
Instead of this i would write (its the same):
if (cantflg) {
...
Freundliche Grüße / Best regards
Günter Ebermann
--
Dipl.-Ing. (FH) Guenter Ebermann, Software Architect, Product
Development Bus Tools
EB - Discover the Experience
Phone: +43 1 59983-95, mailto:[email protected]
Fax: +43 1 59983-18, http://www.elektrobit.com
Elektrobit Austria GmbH, Kaiserstraße 45 / Stiege 2, A-1070 Wien, Austria
Managing Director Otto Fößel
Register Court Vienna, Commercial Register No. FN211944h
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