Notes for the new maintainer: kernel

Alexander E. Patrakov patrakov at ums.usu.ru
Sun May 27 07:03:40 PDT 2007


The kernel on the CD has a special requirement: it has to boot on every 
computer and detect at least the CD and the hard drive. The following 
factors have been identified as trouble-makers:

1) Missing drivers - this means that the CD must use the latest kernel.

2) Drivers that poke ports blindly (this usually means ISA, but I have seen 
a laptop where Knoppix 5.1.1 refuses to boot unless one adds "nopcmcia"). 
This means that the kernel has to be fully modular, and even SCSI drivers 
should be loaded as modules from initramfs, and a mechanism should exist 
that can be used to prevent loading of unwanted drivers. The current SVN 
initramfs does this, the 6.2-5 CD is buggy.

3) libata - there are two drivers for each IDE chipset: the legacy IDE 
driver and a new (since 2.6.20) pata driver that exposes the disks as 
/dev/sdX. The problem is that one must guarantee that the desired one is 
loaded, and this is a difficult thing for the combined ata-piix module (that 
is also responsible for SATA disks). The full switch to libata is 
impossible: while my IDE controller works (driver: pata-via, corresponds to 
the old via82cxxx), Archaic has reported that his controller with the same 
PCI ID and revision doesn't work. This problem is partially solved by the 
"pata" boot argument that blacklists the unneeded modules in the initramfs 
(fixme: piix and jmicron).

4) USB CD-ROMs take some time to be recognized. The current initramfs 
apparently doesn't work with them unless the "rootdelay=10" parameter is passed.

5) ACPI. It is possible to cook the CPU during boot if "fan" is a module.

6) APIC. There are just too many computers with misrouted IRQs 
(manifestation: a device, such as USB controller or a wireless card doesn't 
work) fixable by "linux noapic pci=noacpi".

Less important issues:

1) Drivers that need firmware. If the firmware is not present on the CD, the 
firmware loading process times out, and unload/reload of the driver is 
needed. For this reason, ipw2{1,2}00 drivers are not on the CD (although the 
latest clarification on Intel web site seems to mean that we qualify as ISV 
and thus can redistribute the firmware). And, of course, drivers that need 
firmware cannot be non-modular.

2) iocharset modules: all of them must be built in order for the CD to be 
able to claim good locale support.

-- 
Alexander E. Patrakov



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