I have been using the saa7134.ko and saa7134_dvb.ko drivers for years as
part of my mythtv system, working very nicely.
Now I am trying to use xen to virtualise my mythtv-backend, with PCI
passthrough of the tuner to the virtual machine, everything hasn't gone
smoothly, but I believe I have found an issue within the driver which
would have gone un-noticed on a bare-metal machine, yet which causes a
problem under xen.
Here is what lspci -vvv shows for my card
08:01.0 Multimedia controller: Philips Semiconductors SAA7130 Video
Broadcast Decoder (rev 01)
Subsystem: Compro Technology, Inc. Videomate DVB-T200
Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop-
ParErr- Stepping- SERR- FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium
>TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 64 (21000ns min, 8000ns max)
Interrupt: pin A routed to IRQ 17
Region 0: Memory at febffc00 (32-bit, non-prefetchable) [size=1K]
Capabilities: [40] Power Management version 1
Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA
PME(D0-,D1-,D2-,D3hot-,D3cold-)
Status: D0 PME-Enable- DSel=0 DScale=1 PME-
Kernel modules: saa7134
Notice the MMIO area is 1K in size, but within the driver, it requests
mapping of a 4K area, rather than 1K.
http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.25.y.git;a=blob;f=drivers/media/video/saa7134/saa7134-core.c;h=58ab163fdbd74e628e60655ea05c5d3bea611599;hb=HEAD#l998
Obviously the kernel will have to round the start/end addresses to the
nearest 4K boundaries as this is the granularity of page mapping, but if
the request is too large to begin with it attempts to map two pages,
straddling the card's physical address range, this works on a physical
machine, but fails under xen due to more rigourous checking/enforcement
of permissions.
I have rebuilt the driver module using 0x400 instead of 0x1000 for the
ioremap() size and the driver then loads, instead of failing (I still
have an interrupt problem but will follow that up separately).
If you'd like to follow the discussion I've been having on the xen-devel
list, Keir Fraser should be able to answer questions on why this fails
under xen far better than I can.
http://lists.xensource.com/archives/html/xen-devel/2008-07/msg00004.html
Could you comment on whether you'd accept a patch for this?
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