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[Xen-users] Yes, it does! (Does the amount of main memory influence PCI

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Subject: [Xen-users] Yes, it does! (Does the amount of main memory influence PCI pass through (DMA) capability?)
From: Stephan Austermühle <au@xxxxxxx>
Date: Sun, 09 Aug 2009 21:30:42 +0200
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Hi all,

quoting myself:

> after solving a lot of problems with my DVB-S card it finally ran fine in my 
> domU (3.3.2-rc2, 64 bit, Debian Lenny kernel 2.6.26-2, 64 bit). However, my 
> memory upgrade kit arrived so I upgraded main memory from 16 gbytes to 32 
> gbytes. Since then I have a lot of strange issues which are all looking like 
> no data is transfered from the DVB-S card to the domU. When running the tool 
> "dvbtraffic" I get the following message on the console:
>       cx8802_start_dma() Failed. Unsupported value in .mpeg (0x00000001)
> Does the amount of main memory influence the capability to use DMA transfers?
> I don't see any other error message (xm dmesg, xm log, dom0 logs, domU logs). 
> Do I have a chance to get more debug information on this?

Meanwhile I have cross-checked this problem and can reproduce the problem with 
a standard PC: The above mentioned configuration runs fine with PCI pass 
through with just 2 gbytes of main memory but as soon as the system has 4 
gbytes DVB-S scan does not find data anymore. For me this looks like a DMA 

As describe above I am facing the same problem with my server but with a 16 to 
32 gbytes upgrade.

Does anybody know the technical background for this? Even better: What needs to 
be done to fix this problem?

Kind regards,


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