Low DMA performance leading to "incomplete write to CA"

[Jalle19]

Every now and then I'm getting these errors in dmesg, which lead to "incomplete write to CA" in minisatip, forcing me to restart it (which is where the "DVB CAM detected" messages come from). Does anyone have any idea why this is happening and how to prevent it?

The device in question is a DuoFlex CI.

[887479.736224] ddbridge 0000:06:00.0: IA 1 0 00000007
[887480.019967] ddbridge 0000:06:00.0: l0i2: DMA stalled 1 times!
[887480.019981] ddbridge 0000:06:00.0: l0i2: 2975 packets lost due to low DMA performance!
[887481.528694] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[887482.840274] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1030063.392088] ddbridge 0000:06:00.0: l0i2: 2975 packets lost due to low DMA performance!
[1030064.900133] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1030066.218891] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1120812.742457] ddbridge 0000:06:00.0: l0i2: 2975 packets lost due to low DMA performance!
[1120814.206275] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1120815.518786] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1138248.884437] ddbridge 0000:06:00.0: IA 1 0 00000007
[1138249.014212] ddbridge 0000:06:00.0: l0i2: DMA stalled 1 times!
[1138249.014226] ddbridge 0000:06:00.0: l0i2: 4859 packets lost due to low DMA performance!
[1138250.458866] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1138251.770994] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1138288.054672] ddbridge 0000:06:00.0: l0i2: 4859 packets lost due to low DMA performance!
[1138289.499788] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1138290.817234] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1138327.055096] ddbridge 0000:06:00.0: l0i2: 4859 packets lost due to low DMA performance!
[1138328.480715] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1138329.786153] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1138366.056105] ddbridge 0000:06:00.0: l0i2: DMA stalled 1 times!
[1138366.056119] ddbridge 0000:06:00.0: l0i2: 6557 packets lost due to low DMA performance!
[1138367.481136] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1138368.793608] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully
[1138404.702004] ddbridge 0000:06:00.0: IA 0 0 00000007
[1138405.158824] ddbridge 0000:06:00.0: l0i2: DMA stalled 1 times!
[1138405.158838] ddbridge 0000:06:00.0: l0i2: 8017 packets lost due to low DMA performance!
[1138406.591403] dvb_ca_en50221: dvb_ca adapter 14: DVB CAM detected and initialised successfully
[1138407.909355] dvb_ca_en50221: dvb_ca adapter 15: DVB CAM detected and initialised successfully

[Jalle19]

This is the only mention of this exact issue I've found, and there are no replies: https://www.minidvblinux.de/forum/index.php?topic=10054.0

[Jalle19]

$ sudo modinfo ddbridge | grep -i dma
parm:           alt_dma:use alternative DMA buffer handling (int)
parm:           dma_buf_num:dma buffer number, possible values: 8-32 (int)
parm:           dma_buf_size:dma buffer size as multiple of 128*47, possible values: 1-43 (int)

Should I try fiddling with these?

[catalinii]

Debugging the driver? Tbs6900 driver is quite simple

[Jalle19]

I've looked at the code but it doesn't tell me much

[Jalle19]

Received the following from Digital Devices support:

Hello Sam,

If that happens a few times during the start/stop of adapter usage, then you may skip this warning.
Usually it happens, as in log said-> due to the low DMA (Direct Memory Access) performance
at ARM CPU-based boards, where High CPU usage during DMA operations.

You may try next:
Stop all DVB software.
sudo modprobe -r ddbridge
sudo modprobe ddbridge dma_buf_num=32 dma_buf_size=43

Or via ddbridge.conf:

echo "options ddbridge dma_buf_num=32 dma_buf_size=43" | sudo tee /etc/modprobe.d/ddbridge.conf

and reboot the module or server.

You can also try this:

echo "options ddbridge alt_dma=1 use_workqueue=1" | sudo tee -a /etc/modprobe.d/ddbridge.conf

and reboot as well.

Or both options:
echo "options ddbridge dma_buf_num=32 dma_buf_size=43 alt_dma=1 use_workqueue=1 msi=1" | sudo tee /etc/modprobe.d/ddbridge.conf
sudo update-initramfs -u
sudo reboot

If nothing helps, you need to go to the BIOS:

• change the PCIe link speed,
• switch off IOMMU,
• look for BIOS settings limiting payload size or disabling DMA-related features

And finally, try another PCIe slot.
Could be incorrect lane width (e.g., x1 instead of x4 or x8)

If you have any additional questions, please feel free to ask.
Thank you.