Tested on 15.0-CURRENT as of 2024-01-09, on amd64 with an RME HDSPe RayDAT card. I have this code in use for several months now, as a separate kernel module from ports.

@br: This patch includes the restructured pcm layout and the basic functionality needed for composed pcm devices. The alternative layout that combines all physical ports into one pcm device will be subject to a follow-up patch. I also left out the sysctl settings for sample rate and block size (period).

Since these changes are prerequisite for composed pcm devices, some of the code may be more generic than necessary at this point, e.g. handle multiple physical ports at once. This is also the reason to represent physical ports as bitsets.

Due to ADAT channel width depending on sample rate, DMA slot offset and widths of physical ports change at runtime. These are now encoded in functions instead of table entries.

Variable pcm channel width depending on sample rate cannot be reliably handled by OSS API / pcm device configuration. Therefore we have to support every possible channel width / sample rate combination, see capabilities' format list.

Regarding future support of additional RME cards, I looked briefly into that when I decided for the bitset approach on physical ports. Obviously there's a limit to that (32 bits). But physical ports on the AIO Pro look like the same as AIO, MADI FX has 5 ports and the others have even less. Thus I wouldn't worry too much about this limit, we may have to adapt more aspects of the driver anyway. The linux driver for example handles MADI and AES in separate files from AIO and RayDAT.

looks very good

Thanks. I'll fix the style(9) issues you mentioned and some more that I just spotted now - probably tomorrow.