Re: HauppaugeTV-quadHD DVB-T & HVR5525 mpeg risc op code error

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Ken Smith wrote:



Hi, I'd like to resurrect this thread (copied below). I have a system showing this error. Its a HP ML350 server with 2x Xeon 5675 running Rocky Linux 8.5. It has a Hauppauge HVR5525 card that uses the same cx23885 kernel module as the quadHD card discussed above. The HVR5525 is a dual DVB-T2/DVB-S2 card.

In other threads I read about the dma_reset_workaround option. That option did not appear to be in the version included in standard kernel in Rocky 8.5. I have loaded a 5.4 kernel and compiled the DVB media modules from .git source and set dma_reset_workaround=2 in a file in modprobe.d. The built module shows version 0.0.4

Sadly the error remains. The system runs MythTV v.31. The main symptom is occasional aborted recordings. Although the card does appear to recover, not requiring a reboot/cold restart.

I'd appreciate some assistance with this. What information can I provide to help to trace this.

I'm also maintaining a driver which started to show problems on systems with new CPUs and chipsets quite some time ago, for example on some Ryzen CPUs. In my case it turned out that the problem was because my driver accessed memory locations on a my PCI card directly via a pointer.

Looks like the problem occurred because the CPU/chipset "optimized" and re-ordered the execution of some machine instructions. There are "barrier" instructions that can be inserted in the source code to avoid this, but my original code didn't use them because the driver had been working on many systems for a long time.

Anyway, the low level functions provided by the kernel to access registers on a peripheral are implemented to use those barriers, so simply using those primitives (writel, readl and friends) instead of accessing the registers directly via a pointer (*p = cmd; val = *(p+1) ) fixed the problem for my driver.

All the symptoms described here for the cx23885 module make me assume that the problem is very similar, i.e. due to a missing barrier instruction somewhere in the source code. Unfortunately I'm not familiar with the Linux media driver stuff, so I don't know where I could start to look for a missing barrier instruction.

The only workaround that fixed the problem for me, and that I'm still using, is to load the cx23885 module with a high debug level, by putting a line

options cx23885 debug=8

into a file

/etc/modprobe.d/cx23885.conf

This produces a HUGE amount of kernel log messages (dmesg), but with lower debug levels the driver still didn't work reliably.

To make this stable for a long time, I changed /var/log/ to NOT point to my SSD but to a real hard disk, and I created a cronjob file in /etc/etc/cron.d/ with the line

1 0-23 * * * root rm -f /var/log/kern.log*

to periodically remove the huge kernel log files.

This hack works for me since this has been discussed on this ML years ago.


Martin
Thank you Martin and Robert.

I've been doing some testing today. intel_iommu=off and dma_reset_workaround=2 or dma_reset_workaround=0 didn't change the symptoms.

This system has journald. I initially set debug=1 to see where the messages go and I see what you mean about the volume of messages. I need to work out how to divert this torrent to /dev/null if that option is to be workable.

I fully understand your comment about out of order instructions, Martin. Looks like this driver may need the same attention as the one you maintain. One option for me is to move the HVR5525 to a lower power machine and run that as a slave MythBackend.

Many thanks


Update on this. I have moved the two DVBS2 tuners from the the ML350 Server to a mini PC that has an i3 processor and I'm using that as a MythTV Slave Backend. It has logged three "mpeg risc op code error" events since I started it last Friday and so far no aborted recordings. This is a workaround fix that I'll live with for now. I noticed some recent patches for that module being published.

Thanks Ken

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