2.16 Problems with Linux PnP
But there are a number of things that a real PnP operating system could handle better:
- Allocate bus-resources when they are in short supply by reallocation of resources if necessary
- Deal with choosing a driver when there is more than one driver for a physical device
Since it's each driver for itself, a driver could grab bus-resources that are needed by other devices (but not yet allocated to them by the kernel). Thus a more sophisticated PnP Linux kernel would be better, where the kernel did the allocation after all requests were in. Another alternative would be a try to reallocate resources already assigned if a devices couldn't get the resources it requested.
The "shortage of bus-resources" problem is becoming less of a problem for two reasons: One reason is that the PCI bus is replacing the ISA bus. Under PCI there is no shortage of IRQs since IRQs may be shared (even though sharing is a little less efficient). Also, PCI doesn't use DMA resources (although it does the equivalent of DMA without needing such resources).
The second reason is that more address space is available for device I/0. While the conventional I/O address space of the ISA bus was limited to 64KB, the PCI bus has 4GB of it. Since more physical devices are using main memory addresses instead of IO address space, there is still more space available, even on the ISA bus. On 32-bit PCs there is 4GB of main memory address space and much of this bus-resource is available for device IO (unless you have 4GB of main memory installed).
There was at least one early attempt to make Linux a truly PnP operating system. See http://www.astarte.free-online.co.uk. While developed around 1998 it never was put into the kernel (but probably should have been).
Next Previous Contents
* License
