Subject: Re: Change in PCI behaviour

From: Gary Thomas <[email-masked]>
Date: Tue, 23 Nov 2010 07:44:13 -0700

On 11/22/2010 01:26 PM, Benjamin Herrenschmidt wrote:
> On Mon, 2010-11-22 at 03:01 -0700, Gary Thomas wrote:
>> I have a bit more information on this.  I'm pretty sure that the failures
>> are only happening in my SCSI (SATA actually) code.  My board (8347ea) has
>> a PCI bus with a SIL SATA controller.  This combo works perfectly in 2.6.28.
>> In 2.6.32, it will run for a while (possibly quite a while), then timeout
>> trying to do a large block write - typically 256 blocks.  Once this timeout
>> happens, the SIL controller is stuck and accesses to it will eventually
>> cause the whole system to hang (as above).
>>
>> Was there any major change in how PCI or DMA was handled between 2.6.28
>> and 2.6.32?  Given the ephemeral nature of these failures (multiple runs
>> all eventually fail, but never the same twice), my only hope of fixing it
>> will be to have some ideas what might have changed.
>
> Maybe the changes you did to the PCI outbound windows are now breaking
> DMA ? Make sure the outbound and inbound don't overlap for example and
> that all RAM is reachable for inbound.

Here's what I did to work around this - in my DTS, I set up my PCI as
	ranges = <0x02000000 0x0 0xC4000000 0xC4000000 0x0 0x1C000000
	          0x01000000 0x0 0x00000000 0xB8000000 0x0 0x00100000>;
Before, I had it as
	ranges = <0x02000000 0x0 0xC0000000 0xC0000000 0x0 0x20000000
	          0x01000000 0x0 0x00000000 0xB8000000 0x0 0x00100000>;

I wasn't sure how to reserve the memory (based on your earlier suggestion),
so I just narrowed the window.  Note that I did not change the PCI hardware
registers (maybe the FSL code does?), so the outbound window should still
be the whole 512MB.

If this isn't viable, perhaps you could explain a bit more how to reserve
such a chunk of memory so that the PCI mappings remain the same.

Thanks again

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------