Loading firmware into kernel at boot

andrixnet · 02-20-2014, 06:35 AM

I have found a potential problem with the Slackware distro regarding the kernel drivers requiering firmware files.

Hotplug (/sbin/hotplug) was replaced a long time ago by udev. The problem with udev is that it loads as a userspace daemon too late in the boot process.

Current implementation in the kernel requires a /sbin/hotplug script to load firmware for drivers that require this. If the driver is builtin (not module), this fails.

Read here: /usr/src/linux/Documentation/firmware_class

A sample script is provided, which doesn't seem to work.
copy as /sbin/hotplug, edit the script:

Code:

HOTPLUG_FW_DIR=/lib/firmware/

as this is where the firmware is stored in today's kernels.

Tested on slackware 13.37, 14.0, 14.1

I was able to partially work around the problem by recompiling the kernel and making the FiberChannel adapter (for which I need firmware) as a module. Then udev does the correct work and loads the firmware, the driver loads properly and the device works.

But then I have the problem of udev and lvm starting before the adapter driver loads, and then it is too late for the multipath-tools to remap the devices. I get into a chicken and egg problem which I haven't been able to solve, to this day.

In short: how does one load driver firmware (from /lib/firmware) for builtin drivers at boot, before udev exists?

guanx · 02-20-2014, 07:18 AM

Do you mean the udev in your initrd is not doing the right thing? Or did you disable udev in initrd?

55020 · 02-20-2014, 07:26 AM

Quote:

Originally Posted by andrixnet

In short: how does one load driver firmware (from /lib/firmware) for builtin drivers at boot, before udev exists?

You build the firmware into the kernel.

When you are configuring your custom kernel, look under 'Device Drivers'. Go to 'Generic Driver Options', and under 'Generic Driver Options' there is 'Userspace firmware loading support'. (That name isn't very appropriate in this case, but never mind!)

Under 'Generic Driver Options' there is 'Include in-kernel firmware blobs in kernel binary'. You need to set this to Y.

Also under 'Generic Driver Options' you will need 'External firmware blobs to build into the kernel binary'. Here is the help text for this option:

Quote:

This option allows firmware to be built into the kernel for the case
where the user either cannot or doesn't want to provide it from
userspace at runtime (for example, when the firmware in question is
required for accessing the boot device, and the user doesn't want to
use an initrd).

This option is a string and takes the (space-separated) names of the
firmware files -- the same names that appear in MODULE_FIRMWARE()
and request_firmware() in the source. These files should exist under
the directory specified by the EXTRA_FIRMWARE_DIR option, which is
by default the firmware subdirectory of the kernel source tree.

For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
the usb8388.bin file into the firmware directory, and build the kernel.
Then any request_firmware("usb8388.bin") will be satisfied internally
without needing to call out to userspace.

That's a pretty good description of what you have to do

(The help text also has a warning about redistributing non-GPL firmware, which is the fundamental reason why this is so difficult - you are welcome to blame the hardware companies' lawyers who prefer torturing their customers rather than giving up their illusion of control.)

andrixnet · 02-20-2014, 08:07 AM

Quote:

Originally Posted by guanx

Do you mean the udev in your initrd is not doing the right thing? Or did you disable udev in initrd?

My question is about a system that is already installed and running, to which I added a QLogic FC card.
The boot process is the standard Slackware boot as generated by the installer. It does not use an initrd. (nor do I whish to implement one)

Alien Bob · 02-20-2014, 09:29 AM

If you want to load firmware into the kernel at an early stage, you have to create an initrd and add your firmware to it.

Eric