On 02/03/2014 04:34 PM, Marek Vasut wrote:
On Monday, February 03, 2014 at 09:54:33 PM, Eric Nelson wrote:
Hi Marek,
On 02/03/2014 01:16 PM, Marek Vasut wrote:
On Monday, February 03, 2014 at 08:57:30 PM, Eric Nelson wrote:
[...]
I like having this bit included, but do you need to attribute copyright
for this block?
I'd hate to tempt PCISIG with this portion actually. That's why I didn't put the
whole quotation into the patch either.
[...]
We really should start waving a sign "YOU MUST CONNECT PERST IN YOUR NEW
DESIGN, OTHERWISE A KITTEN DIES!"
Hey, leave the kittens alone!
Are ponies ok? Friendship is magic afterall :-)
Works for me.
We have had success in using/testing PCIe devices without either, but
that doesn't mean we match the spec, and I suppose we'll have to live
with the "broken design" message...
I know. The design without FR works most of the time, but there is one
particular scenario where it may fail (means it fails reliably). I will
assume we have just a simple RC<->EP connection with EP being i82574L
card (well supported and easily available intel NIC):
1) Cold boot the system
2) Bring up the PCIe link in U-Boot
3) Use the e1000e driver for some transfer
4) Boot Linux
5) Bring up the PCIe link in Linux
6) Use the e1000e driver for some transfer
7) Reboot the system from Linux
8) Bring up the PCIe link in U-Boot
In case you don't have means to do FR, your system will fail during 5)
and/or during 8) because in either case, the link and/or EP device can
be in undefined state from previous usage. You are therefore not able to
send in-band messages to the EP (to issue hot reset for example*) nor
restart the link, thus you're trapped.
* if you try to send anything over unstable PCIe link on MX6, it can
stall your entire system to the point where the system bus is stuck and
not even JTAG debugger can halt the CPU (!)
Thanks. That's a useful test scenario.
Hope it helps :) Sometimes you need to do a few cycles until the hardware hangs.
I found this out when I was debugging another custom board here. I think we will
have a rock-solid PCIe implementation on MX6 for 3.14 and 2014.04 ;-)
You can bet on a knee-jerk reaction at design reviews here in Arizona...
Regards,
Eric
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