[Letux-kernel] OMAP4/5 AESS on v6.4

[H. Nikolaus Schaller]

Hi Tony and Peter,
I have upgraded my WIP tree to v6.4-rc3 now.

It is almost working, firmware can be built, and is loaded, subdevices are presented, graph
has been verified against the working 3.15 version, legacy sound works, amixer settings are
fine, etc.

The last remaining issue (before the next reveals itself) is that the AE DSP isn't running.
Playing a sound gets stuck in wait_for_avail() in sound/core/pcm_lib.c obviously waiting for 
some interrupt or DMA trigger from the DSP.

Kernel log/user-space symptoms are:

[   36.957956] omap-abe-twl6040 sound: playback write error (DMA or IRQ trouble?)
play WARN alsa: Input/output error

So it may either be a clocking or power issue or something with initialization.
Very difficult to find. Also symptomatic seems to be that I can hex-dump the /sys/kernel/debug
files for cmem, dmem, and smem but not pmem.


Therefore I am currently going once again through all questionable code where I
had noted a FIXME to tell that it is obviously not compatible to modern
kernels and has not yet been fixed.


One such place is

https://git.goldelico.com/?p=letux-kernel.git;a=blob;f=sound/soc/ti/aess/omap-aess-pcm.c;h=e9c8b9a00f032f336cac8cbb7e441ce8a7476507;hb=74db6d179bad60cdad29a8704f9e606f8cffccd3#l673

where there is a "context-lost mechanism" which was removed in v4.18.

Any ideas what that "context lost" is or how it can be fixed in modern kernels?


You may also try or review the full tree:

https://git.goldelico.com/?p=letux-kernel.git;a=shortlog;h=refs/heads/aess-6.4-rc3

I haven't tried that as a stand-alone without my other local Letux patches for my
devices, but I think it can run at least on PandaES and omap5uevm after configuring
omap2plus_defconfig.

Building firmware is best done on the device and running a script like this one:

https://git.goldelico.com/?p=letux-kernel.git;a=blob;f=Letux/root/build-aess-fw;h=0bfe59559e5395fb1e5ad32bbbac676d7665aa22;hb=refs/heads/letux-current

This clones the kernel git repo and tries to build the firmware on the target device.
I have only tested on Debian 9.13. Other releases may reveal subtle conflicts in system
include files...


Any help (also by readers) to get this beast finally working is welcome.

Best regards,
Nikolaus