rjrbytes at gmail
Sep 23, 2012, 6:03 PM
Post #5 of 5
On Sun, Jul 8, 2012 at 4:56 PM, Andy Walls <awalls [at] md> wrote:
> On Sun, 2012-07-08 at 15:28 -0400, Andy Walls wrote:
>> On Sat, 2012-07-07 at 12:44 -0500, Robert Rust wrote:
>> > After weeks of headaches trying to get my HVR-1600 to work, I finally
>> > determined with help from this list that the H77 chipset on my
>> > motherboard was the root of my problems, so I replaced the board. I
>> > am now trying to set up my MythTV backend in a Xen domU after
>> > verifying that it can capture outside of Xen and in the Xen dom0 host.
>> What is the difference between Xen domain dom0 and domU (for a Xen newb
>> like me)?
> Ah, found it:
> "... Domain 0) is a specialized Virtual Machine that 0 has special
> privileges like the capability to access the hardware directly, handles
> all access to the system’s I/O functions ..."
> "... Xen [domU] guests are totally isolated from the hardware: in other
> words, they have no privilege to access hardware or I/O functionality.
> Thus, they are also called unprivileged domain (or DomU)."
>> > I can tune to channels and I get data when I cat /dev/video0 ... but
>> > the data doesn't seem to be valid video.
>> > Does anybody have input on how I can work towards a resolution on
>> > this?
> This page looks helpful:
> If your linux kernel panics because the cx18 driver asks for more DMA
> buffer space than the SWIOTLB (Software IOMMU) in Linux can provide, you
> can cut down on the number and size of buffers for CX23418 data streams
> using cx18 module options.
> Also the Linux Software IOMMU requires copies of DMA buffres by the CPU,
> so performance will stink, unless you have lots of excess horsepower.
> Please note that the CX23418 acts as a DMA master on the PCI bus. When
> the cx18 driver tells the CX23418 about where the DMA buffers are, they
> must be the correct PCI address-space addresses that the CX23418 chip
> and firmware can actually DMA into. If you have a Linux kernel running
> in any other Xen (dom0 or domU) guest, you should probably blacklist the
> cx18 driver in that guest, so that instance of the cx18 driver doesn't
> also load the CX23418 with DMA addresses to use or otherwise change the
> CX23418's System Control Block (SCB) area.
> (In case you are interested, this is the function in the cx18 driver
> where the driver tells the firmware about the DMA addresses of buffers:
> and this is the function that initializes the SCB on driver probe:
Would this preclude passing a second HVR-1600 to a different DomU ?
DomU #2 sees the HVR-1600 and loads the cx18 module for it, but I
can't capture valid video. If you're wondering why I don't pass it to
DomU #1 (in which the first HVR-1600 works fine), I can't seem to get
DomU #1 to see both cards at once.
In DomU #2, I get messages like the following:
Sep 23 16:23:59 merry kernel: [ 1131.227956] cx18-0: Skipped encoder
MPEG, MDL 9, 62 times - it must have dropped out of rotation
Thoughts? I'm also going to try pursuing why I can't pass both cards
to one DomU.
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