MPC85xx PCI transfer disconnect

[Liu Dave-r63238]

> I know this is probably a question for Freescale directly, 
> but I thought I would post here to see if anyone else has 
> seen similar issues with the MPC85xx PCI under Linux.
> 
> I'm using a Freescale MPC85xx (8541) processor and seeing an 
> extreme slowness to the PCI bus.
> 
> I'm attemping to do 2048 byte PCI burst reads from an 
> external PCI master.  So an external chip is the PCI master 
> ("initiator") and the MPC85xx is the PCI slave ("target")
> 
> When initiating the PCI burst read, there is a 270 ns delay 
> from the MPC85xx claiming the transaction (DEVSEL# going low) 
> to being ready (TRDY# going low).  Then 64 bytes (a single 
> cacheline) are transferred, and TRDY# goes inactive.  Next, 
> STOP# goes low, terminating the transfer.  I believe this is 
> considered a PCI DISCONNECT type 1 since IRDY# is active the 
> entire time.
> 

The 85xx cacheline is 32 bytes. 
Did you enable Memory Read Multiple command of your PCI master?

> What I would expect is that the entire 2048 bytes are 
> transferred in one PCI bus mastership, but instead there are 
> several re-arbitrations and long delays in between several 64 
> byte transfers.
> 
> Additional info:
> The PCI bus is 64bit running at 66 MHz.
> I'm running a modified Linux 2.6.9 kernel (elinos-111).
> The PCI CCSR piwar1 = 0xa0f4401d.
> 
> Freescale has an FAQ 21021 that describes having a PCI 
> DISCONNECT 2, which sounds similar to my problem, but I've 
> already confirmed I'm doing what the FAQ suggests (enable 
> prefetching in the piwar register)
> (http://www.freescale.com/webapp/sps/utils/SingleFaq.jsp?FAQ-2
1021.xml)

Any thoughts/suggestions would be appreciated,
Tim
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