What is the minimal set of firmware files I need for my hardware?

[Greg KH]

On Mon, May 04, 2020 at 03:56:40PM +0300, Doron Behar wrote:
> On Mon, May 04, 2020 at 12:45:55PM +0200, Greg KH wrote:
> > On Mon, May 04, 2020 at 01:26:35PM +0300, Doron Behar wrote:
> > > I hope this question fits to this List.
> > > 
> > > Today I learned that my distro's `linux-unfree-firmware` package is 491
> > > Mb in size. I'm pretty sure my hardware doesn't need all of these files.
> > > Maybe different Linux distros call this package differently, but I'm talking
> > > about the firmware files that come from:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/
> > > 
> > > I think I can reduce this disk usage if I'll only know what files
> > > I can exclude from there.
> > > 
> > > Is there any official documentation, that states exactly what files from
> > > That git repo are needed per device / computer model? Perhaps the official
> > > documentation of my Computer's hardware will state that? There's a Linux
> > > from scratch webpage[1] that gives some info for popular hardware, but I'm
> > > wondering if there's a bit more "official" information available
> > > somewhere.
> > > 
> > > [1]: http://linuxfromscratch.org/blfs/view/svn/postlfs/firmware.html
> > 
> > The kernel macro MODULE_FIRMWARE() will show the firmware file that a
> > specific kernel module needs.  So if you look a the output of modinfo
> > for all of the modules that your system needs, you will see a "firmware"
> > line that shows the name that your hardware needs for that specific
> > driver/module.
> 
> Thanks for replying greg,
> 
> So I have the command `modinfo` available, should I just iterate _all_
> the files in /usr/lib/modules/5.6.7/kernel ? For example:

No, don't iterate all kernel modules, unless you only built the modules
that you know you need for your hardware (like you can get by running
'make localmodconfig').

> 
> ```
> $ modinfo /usr/lib/modules/5.6.7/kernel/net/ieee802154/ieee802154.ko.xz
> filename:       /usr/lib/modules/5.6.7/kernel/net/ieee802154/ieee802154.ko.xz
> author:         Dmitry Eremin-Solenikov
> description:    IEEE 802.15.4 configuration interface
> license:        GPL v2
> depends:        
> retpoline:      Y
> intree:         Y
> name:           ieee802154
> vermagic:       5.6.7 SMP mod_unload 
> sig_id:         PKCS#7
> signer:         
> sig_key:        
> sig_hashalgo:   unknown
> signature:      
> ```
> 
> Doesn't seem informative regarding firmware files. Should I expect other
> .ko.xz files to give a line with `firmware: `?

Yes, try looking at btrtl.ko for an example.

The module you picked above does not need any firmware to control the
hardware it manages (hint, it's not a driver for any specific hardware,
just a protocol that other drivers use.)

> Plus, how do I know what modules does my system need and which it
> doesn't?

That's up to you to figure out if you are building your own kernel
image.

As I mentioned above, the 'make localmodconfig' is a nice quick shortcut
to get that done, I recommend using it by doing:
	- boot a distro kernel
	- plug in all devices you want to support
	- run 'make localmodconfig' to create a .config file based only
	  on the modules you have loaded in the system at that point in
	  time.
	- build the kernel with that .config file

hope this helps,

greg k-h