[U-Boot] [PATCH] pci: mx6: Implement reset callback

[Marek Vasut]

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 :-)

> >> 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 ;-)

Best regards,
Marek Vasut