Eran Liberty wrote:
This should probably go to the Freescale support, as it feels like a
hardware issue yet the end result is a very frozen Linux kernel so I
post here first...
I have a programmable FPGA PCIe device connected to a Freescale's
P2020 PCIe port. As part of the bring-up tests, we are testing two
faulty scenarios:
1. The FPGA totally ignores the PCIe transaction.
2. The FPGA return a transaction abort.
Both are plausible PCIe behavior and their should be outcome is
documented in the PCIe spec. The first should be terminated by the
transaction requestor timeout mechanism and raise an error, the second
should abort the transaction and raise and error.
In P2020 if I do any of those the CPU is left hung over the transaction.
something like:
in_le32(addr)
is turned into:
7c 00 04 ac sync 7c 00 4c 2c lwbrx r0,0,r9
0c 00 00 00 twi 0,r0,0
4c 00 01 2c isync
assembly code, where in r9 (in this example) hold an address which is
physically mapped into the PCIe resource space.
The CPU will hang over the load instruction.
Just for the fun of it, I have wrote my own assembly function omitting
everything but the load instruction; still freeze.
Replace "lwbrx" with a simple "lwz"; still freeze.
It looks like the CPU snoozes till the PCIe transaction is done with
no timeouts, ignoring any abort signal.
I am going to:
A. Try to reach the Freescale support.
B. Asked the FPGA designed to give me a new behavior that will stall
the PCIe transaction replay for 10 sec, but after those return ok.
C. report back here with either A or B.
If you have any ideas I would love to hear them.
-- Liberty
Some more info:
As said the the FPGA designer provided me a PCIe device that will stall
its response to a variable amount of time. The CPU became un-frozen
after this amount of time. More over, we have found that in that period
till it un-froze the PCIe core did a retry to that transaction over and
over every 40 ms. This gave me the bright idea to look for the word
"retry" in the Freescale documentation which rewarded me with these
registers:
------------------------------------------------------- snip
-------------------------------------------------------
16.3.2.3 PCI Express Outbound Completion Timeout Register
(PEX_OTB_CPL_TOR)
The PCI Express outbound completion timeout register, shown in Figure
16-4, contains the maximum wait
time for a response to come back as a result of an outbound non-posted
request before a timeout condition
occurs.
Offset
0x00C
Access: Read/Write
0 1 5 7
8
31
R
TD
â TC
W
Reset 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Figure 16-4. PCI Express Outbound Completion Timeout
Register (PEX_OTB_CPL_TOR)
Table 16-6 describes the PCI Express outbound completion timeout
register fields.
Table 16-6. PEX_OTB_CPL_TOR Field
Descriptions
Bits Name
Description
0 TD Timeout disable. This bit controls the
enabling/disabling of the timeout function.
0 Enable completion timeout
1 Disable completion timeout
1â7 â Reserved
8â31 TC Timeout counter. This is the value that is used to
load the response counter of the completion timeout.
One TC unit is 8Ã the PCI Express controller clock
period; that is, one TC unit is 20 ns at 400 MHz, and 30
ns at 266.66 MHz.
The following are examples of timeout periods based
on different TC settings:
0x00_0000 Reserved
0x10_FFFF 22.28 ms at 400 MHz controller clock; 33.34
ms at 266.66 MHz controller clock
0xFF_FFFF 335.54 ms at 400 MHz controller clock;
503.31 ms at 266.66 MHz controller clock
16.3.2.4 PCI Express Configuration Retry Timeout Register
(PEX_CONF_RTY_TOR)
The PCI Express configuration retry timeout register, shown in Figure
16-5, contains the maximum time
period during which retries of configuration transactions which resulted
in a CRS response occur.
Offset
0x010
Access: Read/Write
0 1 3
4
31
R
RD â TC
W
Reset 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1
Figure 16-5. PCI Express Configuration Retry Timeout Register
(PEX_CONF_RTY_TOR)
QorIQ P2020 Integrated Processor Reference
Manual, Rev. 0
16-12
Freescale Semiconductor
PCI Express Interface Controller
Table 16-7 describes the PCI Express configuration retry timeout
register fields.
Table 16-7. PEX_CONF_RTY_TOR Field Descriptions
Bits Name Description
0 RD Retry disable. This bit disables the retry of a
configuration transaction that receives a CRS status response
packet.
0 Enable retry of a configuration transaction in response
to receiving a CRS status response until the timeout
counter (defined by the PEX_CONF_RTY_TOR[TC] field)
has expired.
1 Disable retry of a configuration transaction regardless
of receiving a CRS status response.
1â3 â Reserved
4â31 TC Timeout counter. This is the value that is used to load
the CRS response counter.
One TC unit is 8Ã the PCI Express controller clock
period; that is, one TC unit is 20 ns at 400 MHz and 30 ns
at 266.66 MHz.
Timeout period based on different TC settings:
0x000_0000 Reserved
0x400_FFFF 1.34 s at 400 MHz controller clock,
2.02 s at 266.66 MHz controller clock
0xFFF_FFFF 5.37 s at 400 MHz controller clock,
8.05 s at 266.66 MHz controller clock
------------------------------------------------------- snap
-------------------------------------------------------
Now this is all nice on the paper, but what the P2020 seems to be doing
in reality is
1. never expire
2. do re-tries even in the non configuration access
I am going to try to disable completion timeout and see if I get better
behavior.
-- Liberty
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