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Re: How the kernel firmware loader works

On Sat, Jan 07, 2006 at 12:05:48AM +0100, Marco d'Itri wrote:
> (#104) How the kernel firmware loader works
> fEnIo[0] learnt an important lesson about the kernel firmware loader:
> it (usually) does not work as expected for non-modular drivers.

Yeah... thanks a lot for your explanation. I'm now a little smarter.
> The reason is that the request_firmware()[1] interface is synchronous.
> Since it's usually called in the initialisation section of drivers, the
> userspace firmware loader is not available yet if the calling driver is
> built-in in the kernel. The request_firmware_nowait()[2] asynchronous
> interface was designed to replace it, but most drivers have not been
> ported yet.
> When a driver calls request_firmware(), a uevent[3] is sent by the
> kernel to udev over a netlink(7) socket, requesting that a specific
> file is uploaded. udevd runs /lib/udev/firmware.agent, a simple shell
> script which will look for the $FIRMWARE file in a few directories and
> then copy it to the designated place in the driver $DEVPATH in sysfs.
> If the driver is initialised before userspace is started then the
> loader will not be available, and the request will fail. A possible
> solution is to run udev in the early userspace environment (initramfs),
> but just compiling the driver as a module is usually simpler.

So I suppose that it shouldn't be possible to compile in such drivers, if
they work only as a module. At least since they aren't ported to new

Anyway, once again thanks for explanation, and now I'm glad that I posted
this question in blog, otherwise I would probably lost more time to figure
out what's going on.


  ,''`.  Bartosz Fenski | mailto:fenio@debian.org | pgp:0x13fefc40 | irc:fEnIo
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 `. `'           phone:+48602383548 | proud Debian maintainer and user
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