ACPI root pointer from UEFI System Table.

As I found out after I posted my lat entry , the correct way to find the Root pointer for the ACPI tables is to get it from the EFI System table. Where does that get set? Here’s the general flow: again, we start at init/main.c. start_kernel.   However, the call is not in the ACPI code, but rather in setup_arch. The call chain goes

start-Kernel->setup_arch->efi_init->efi_get_fdt_params and that seems to pull it our of initial_boot_params. I can’t quite see where that is initialized. Yet. From context it looks like it is constructed out of the kernel command line parameters. Still learning….

Learning ACPI for ARM64 part 1: Finding the Root.

It started as a request from our tech lead: please help triage these patches. So I lookedat the set of patches and started with what looked like the simplest one:

Fix topology for Core scheduling.

It *just* reorders the code to call

store_cpu_topology(cpu);
before
notify_cpu_starting() .

Yeah…there is no such thing as a simple patch. These are my notes as I study and learn ACPI. My assumptions are here for all to see, and may well prove to be wrong.

Lets dig in.

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Building Linux tip-of-tree on an Ampere based system

I Have an Ampere Altra-Max/INGRASYS Yushan Server System running Centos 8 stream.

Because we are a chip manufacteror, we don’t sell end systems, we provide a reference platform that is a starting point for our customers to make a product. This leads to bizarre set of internal versus external names. One thing that you can rely on, however, is the identifier of the processor itself:

# cat /proc/cpuinfo 
processor	: 0
BogoMIPS	: 50.00
Features	: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs
CPU implementer	: 0x41
CPU architecture: 8
CPU variant	: 0x3
CPU part	: 0xd0c
CPU revision	: 1
...

TO make this readable, use the utility lscpu:

[root@eng14sys-r
111 ~]# lscpu 
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              80
On-line CPU(s) list: 0-79
Thread(s) per core:  1
Core(s) per socket:  80
Socket(s):           1
NUMA node(s):        1
Vendor ID:           ARM
BIOS Vendor ID:      Ampere(R)
Model:               1
Model name:          Neoverse-N1
BIOS Model name:     Ampere(R) Altra(R) Processor
Stepping:            r3p1
CPU max MHz:         3000.0000
CPU min MHz:         1000.0000
BogoMIPS:            50.00
L1d cache:           64K
L1i cache:           64K
L2 cache:            1024K
NUMA node0 CPU(s):   0-79
Flags:               fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs


I want to build the latest Linus-repo Linux Kernel and run it on the server. Here’s the steps I went through.

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Unifying Audio with Pipewire

ALSA. Jack. PulseAudio. MIDI. Musescore. Jamulus.

My musical interactions with Linux are not the most complex in the world, but they ain’t trivial. The complexity of the Linux audio landscape has been a stumbling block so far. Pipewire has just gotten me past that.

The title of this article implies that you need to do something other than install Pipewire. So far, this is not true. On my system, at least, it Just works.

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