dump IPC message payload to dmesg

[xiulipan]

Dump IPC message payload to help debug and reproduce IPC message.

[wenqingfu]

Do we still need this feature? @xiulipan

[ranj063]

@wenqingfu yes we do need this feature. This will be very helpful in making sure the IPC payload isnt tainted before it is sent to the DSP

[lyakh]

I actually wanted to have a "dump IPC" feature but for a completely different reason - to use a live system to record topology IPC messages to then create an object from those messages to be integrated with the DSP firmware image for the host-less mode. But I would actually use something different than the kernel logging for that. Something like debugfs / /proc / netlink or even a new ioctl to an existing device node... But I'm not sure how IPCs can be tainted - don't we have a much larger problem if IPC messages can be tainted on a system? @ranj063 could you clarify?

[ranj063]

@lyakh I do not think they are. This is related to the issue thesofproject/sof#766.

[xiulipan]

@lyakh
Actually this feature originally is about reproduce some bug on host-less DSP on QEMU or some other simulator. And I think that is just what you think?
@ranj063
Good point! I think this will also have benefit about this kind of bugs. To help us make sure the payload is what we expect.

[lyakh]

@ranj063 @xiulipan @wenqingfu what if we do this as a debugfs file with a blocking read? I'm not a huge fan of polluting the kernel log with potentially many (dozens? hundreds?) messages per second.

[xiulipan]

@lyakh
The point is that, we could not know when to read the payload from debugfs. The IPC is pretty quick to send.
Or you suggest we have another debugfs to store all IPC message in history order?

[lyakh]

@xiulipan it would be a different debugfs file, sure, similar to the logger. Yes, you would have to capture it explicitly, it wouldn't be saved automatically, and it would be more difficult to synchronise IPC messages with the rest of debugging output. So, we have to weigh the pros and the cons.

[xiulipan]

@lyakh
That sound reasonable.
And if we could know what is the input date format for the host-less DSP system, then we can directly output in that format.