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….

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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