Linux 2.4 Spotlight: ISA Plug-and-Play

An amazing number of features are new or improved under (what will be) Linux 2.4. In my article last month, “Bullet Points: Linux 2.4”, I described a number of these features. The one feature which I feel will most change the face of distributions in the years to come (if only in terms of their support for legacy devices) is ISA Plug-and-Play support.

Back in the good old days (before PCI became the standard bus architecture for Intel-class PCs), buses weren't very smart in and of themselves. Plug-and-Play features were largely not present in these older machines. It was expected that if you owned the machine, you more or less understood exactly what hardware was in it and exactly where each device “lived” in the computer innerspace. Adding a new sound card, for example, was often an exercise in “put in—reboot—pull out—change jumpers—repeat”, as the vast majority of ISA cards required hardware jumpers or something similar to be configurable. This situation was not very good for consumer users of PCs, whose understanding of their machines' internals was slowly degrading to the point at which new users were hardly expected to know where to plug in the mouse.

In conference rooms of computer manufacturers around the world, meetings were held and standards debated over how this user barrier could be overcome. (At least, that's how it happened in my personal universe.) Sure, having a better bus would be nice, but that would require things to change. Some bright soul got the idea to band-aid the situation via a standard in configurable cards which could be configured by a wise BIOS or operating system. The ISAPNP “standard” was thus born.

ISAPNP filled in all those Plug-and-Play gaps we suffered from in the ISA world. No longer would we have to blindly probe for devices, as they would happily announce themselves (more or less) to anyone who would listen. No longer would we be forced to change jumper settings, as instead we had a neat DOS utility to do that for us. But that was the real crux of the problem: PnP-compatible quickly came to mean “DOS/Windows only”, as other operating systems of the time found they could not speak the magic language of the PnP specification. Linux, too, fell into this trap; it was often advised that one should initialize his or her cards under DOS and (soft) reboot into Linux to make things work.

Fortunately, if you give the Linux community a problem, it isn't long until a solution of some kind can be found. For some, loadlin and a DOS partition were still the only answer, but for others there were the ISA PnP utilities which were, until recently, the way to configure PnP devices under Linux and elsewhere. This utility, handy as it is, is a pain for many users to figure out. It requires users to resolve resource conflicts on their own. It requires drivers to be compiled as modules so they can be loaded after the user space utility had run. Over time, the interface to this utility improved; it could even do a decent job of autoconfiguring cards. Distributions started supporting it and masking its functionality under a protective shield of pretty dialog boxes so that even the clueless could stand a chance at getting it to work. Still, it was not a perfect solution.

Linux 2.4 will, for the first time, support ISA PnP devices internally. No longer will a user space utility be required to configure cards to be used; the kernel itself can now do it. Generally, this is to be done transparently: the serial driver or the soundblaster driver will simply do a search for PnP devices in the same way they now search for and configure PCI devices. When a compatible device is found, the kernel can configure and activate it and pass the resources it uses on to the driver responsible. The kernel can even handle resource conflicts. Of course, there are probably settings and configurations which the kernel will not get right, and there will always be the option to “fall back” to the old user-space-by-hand configuration. But this, in my opinion, is a great step forward for desktop Linux.

Now, the warnings: Linux 2.4 isn't even released yet, so how can you take advantage of these remarkable new features in your machines? You can download a snapshot of the latest Linux 2.3 (developers only) kernel and compile it for your system. Will it work? Probably. Will it support your cards? Well, maybe not. If you're a programmer, there isn't a better time to get involved with Linux 2.3 development and help the mainstream kernel hackers squash the bugs to make Linux 2.4 the best Linux ever. If you're not a programmer, you can help just by downloading, compiling and installing a recent kernel and reporting the results. Linux is developed by the community, and as we approach the next stable milestone, it is the community members who can make a difference. Next time you are sitting in front of your computer trying to tweak your isapnp.conf to work with your new modem, think of those brave souls behind their keyboards who work so hard to make Linux the best damn operating system it can be and give them a hand.