Gated from my blog.
(#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. 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. [0] http://jabba.uaznia.net/fEnIo/id/8689 [1] http://lxr.linux.no/ident?i=request_firmware [2] http://lxr.linux.no/ident?i=request_firmware_nowait [3] http://lxr.linux.no/ident?i=kobject_uevent Posted at 23:57:34. [http://blog.bofh.it/id_104] ----------------------------------------------------------------------------- -- ciao, Marco -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
