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The_Great_Sephiroth
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PostPosted: Sat Sep 28, 2019 10:14 pm    Post subject: How to figure out which kernel features to use? Reply with quote

I know how to build kernels and have been doing so for some time, but some things still linger. For example, how do I know if my CPU supports things like Intel LPSS? I imagine it does but can find no guidance on this. There are many options in the kernel configuration for things which I would like to use if my hardware supports it. I generally start with an all NO config and turn on only what I need, building permanent pieces of hardware into the kernel, such as the soundcard and video card on a laptop. Other things (USB devices) I build as modules. I know how to identify firmware and microcode to be loaded into the kernel (built in) for devices such as the CPU or a wireless card. However, LPSS, among others, eludes me. Can somebody help me out here?

*UPDATE*

Here is another question. How the heck do I figure what what version of ACPI I have? I have been inside of /sys/firmware/acpi/, googled until my eyes bled, and looked around the BIOS/EFI and cannot figure out what the ACPI version is on the new laptop. If it is 4.0 or newer I want to enable support in my kernel.
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The_Great_Sephiroth
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PostPosted: Wed Oct 09, 2019 12:32 am    Post subject: Reply with quote

So nobody can explain how to determine a systems ACPI version?
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Tony0945
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PostPosted: Wed Oct 09, 2019 12:52 am    Post subject: Reply with quote

Haven't a clue about ACPI.
You could start with pappy's configs. There is a link somewhere in the forums.
NeddySeagoon has linked several times and I think at one time he hosted a mirror.
I recall seeing an update sometime this year.
I'd try googling "pappy's configs forums.gentoo" but I'm lousy at googling.
I started with the genkernel config around ten years ago. Once I did a meld with pappy's config.
After than I made all modules and then remade removing the modules that didn't load.
Very unscientific.
My advice is to start with pappy's configs and always run make oldconfig when updating kernel version.

I gather it's an art, not a science.
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javeree
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PostPosted: Wed Oct 09, 2019 7:51 am    Post subject: Reply with quote

Sometimes I just enable a kernel item, restart and see if I get any new output in dmesg telling me that something was detected or not. I agree that there is often no way to know what is in your PC exactly. E.g. I2C devices don't announce themselves, so you will not see them through lspci/lsusb/... (there is no lsi2c), and even to detect them, you basically need to know how they are used, write some code to use them and see if there is a reaction (e.g. try to write a value and then read the same value). There is no one size fits all.

for these HW related topics, I tend to go with 'if in doubt enable or make modular'.

For SW related topics (e.g. filesystems, networking option), I try to understand what the feature does and enable depending on if I want it. Here I generally go with 'if in doubt disable or make modular'
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krinn
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PostPosted: Wed Oct 09, 2019 10:45 am    Post subject: Re: How to figure out which kernel features to use? Reply with quote

The_Great_Sephiroth wrote:
Can somebody help me out here?

Well, no idea of how to do that properly, i'll gives you "my way".

As most "weird/unknown features" need hardware specific they fall under udev hands, so the solution is just from time to time, building a kernel with everything as module, run it, and see what modules were loaded because you have an hardware that use the feature.
Code:
lsmod | grep aesni
aesni_intel           184320  0
aes_x86_64             20480  1 aesni_intel
crypto_simd            16384  1 aesni_intel
cryptd                 20480  2 crypto_simd,aesni_intel
glue_helper            16384  1 aesni_intel

Code:
module-name.sh | grep aesni
aesni_intel: Rijndael (AES) Cipher Algorithm, Intel AES-NI instructions optimized

I wouldn't had know that my cpu could use that else.
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TheLexx
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PostPosted: Wed Oct 09, 2019 2:03 pm    Post subject: Reply with quote

What I try from time to time, especially when getting a major hardware upgraded or a major kernel upgrade is to, see what happens when I boot a different live distro. Many live distros are quite good at detecting different hardware features. While none may be perfect, the combination of more than one works well. If one distro misses something, the other often picks it up. I can then save the dmesg, lsmod, lspci -k -v, lsusb from each distro to refer back to from time to time.

I find it more reliable that a distro will uncover "hidden" features than me just poking around in the dark.

Most distros also enable /proc/config.gz although it is usually not needed, it is sometimes a good thing to have saved rather than having to re-boot just to get it.
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The_Great_Sephiroth
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PostPosted: Mon Oct 14, 2019 12:11 am    Post subject: Reply with quote

I know how to build my kernel modules cor hardware. The issue is the ACPI version, or obscure things like Intel LPSS. I figured out LPSS from an Intel document, but no clue on my ACPI version.
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krinn
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PostPosted: Mon Oct 14, 2019 1:15 pm    Post subject: Reply with quote

The_Great_Sephiroth wrote:
I know how to build my kernel modules cor hardware. The issue is the ACPI version, or obscure things like Intel LPSS. I figured out LPSS from an Intel document, but no clue on my ACPI version.

Except like this, no idea:
Code:
[    0.001000] ACPI: Core revision 20170728

https://uefi.org/specifications
so 6.2 errata A for me
ps: but it could be the linux acpi version support and not the one from my bios, acpi is really blur :)
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