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diff --git a/Documentation/mca.txt b/Documentation/mca.txt new file mode 100644 index 000000000..62b777de4 --- /dev/null +++ b/Documentation/mca.txt @@ -0,0 +1,210 @@ +i386 Micro Channel Architecture Support +======================================= + +MCA support is enabled using the CONFIG_MCA define. A machine with a MCA +bus will have the kernel variable MCA_bus set, assuming the BIOS feature +bits are set properly (see arch/i386/boot/setup.S for information on +how this detection is done). + +Adapter Detection +================= + +The ideal MCA adapter detection is done through the use of the +Programmable Option Select registers. Generic functions for doing +this have been added in include/linux/mca.h and arch/i386/kernel/mca.c. +Everything needed to detect adapters and read (and write) configuration +information is there. A number of MCA-specific drivers already use +this. The typical probe code looks like the following: + + #include <linux/mca.h> + + unsigned char pos2, pos3, pos4, pos5; + struct device* dev; + int slot; + + if( MCA_bus ) { + slot = mca_find_adapter( ADAPTER_ID, 0 ); + if( slot == MCA_NOTFOUND ) { + return ENODEV; + } + /* optional - see below */ + mca_set_adapter_name( slot, "adapter name & description" ); + mca_set_adapter_procfn( slot, dev_getinfo, dev ); + + /* read the POS registers. Most devices only need + 2 and 3 */ + pos2 = mca_read_stored_pos( slot, 2 ); + pos3 = mca_read_stored_pos( slot, 3 ); + pos4 = mca_read_stored_pos( slot, 4 ); + pos5 = mca_read_stored_pos( slot, 5 ); + } else { + return ENODEV; + } + + /* extract configuration from pos[2345] and set everything up */ + +Loadable modules should modify this to test that the specified IRQ and +IO ports (plus whatever other stuff) match. See 3c523.c for example +code. + +Keep in mind that devices should never directly access the POS registers +(via inb(), outb(), etc). While it's generally safe, there is a small +potential for blowing up hardware when it's done at the wrong time. +Furthermore, accessing a POS register disables a device temporarily. +This is usually okay during startup, but do _you_ want to rely on it? +During initial configuration, mca_init() reads all the POS registers +into memory. mca_read_stored_pos() accesses that data. mca_read_pos() +and mca_write_pos() are also available for (safer) direct POS access, +but their use is _highly_ discouraged. mca_write_pos() is particularly +dangerous, as it is possible for adapters to be put in inconsistent +states (i.e. sharing IO address, etc) and may result in crashes, toasted +hardware, and operator injury. + +User level drivers (such as the AGX X server) can use /proc/mca to find +adapters (see below). + +Some MCA adapters can also be detected via the usual ISA-style device +probing (many SCSI adapters, for example). This sort of thing is highly +discouraged. Perfectly good information is available telling you what's +there, so there's no excuse for messing with random IO ports. However, +we MCA people still appreciate any ISA-style driver that will work with +our hardware. You take what you can get... + +Level-Triggered Interrupts +========================== + +Because MCA uses level-triggered interrupts, a few problems arise with +what might best be described as the ISA mindset and its effects on +drivers. These sorts of problems are expected to become less common as +more people use shared IRQs on PCI machines. + +In general, an interrupt must be acknowledged not only at the ICU (which +is done automagically by the kernel), but at the device level. In +particular, IRQ 0 must be reset after a timer interrupt (now done in +arch/i386/kernel/time.c) or the first timer interrupt hangs the system. +There were also problems with the 1.3.x floppy drivers, but that seems +to have been fixed. + +IRQs are also shareable, and most MCA-specific devices should be coded +with shared IRQs in mind. + +/proc/mca +========= + +I did a major rewrite of /proc/mca. It is now a directory containing +various files for adapters and other stuff. + + /proc/mca/pos Straight listing of POS registers + /proc/mca/slot[1-8] Information on adapter in specific slot + /proc/mca/video Same for integrated video + /proc/mca/scsi Same for integrated SCSI + /proc/mca/machine Machine information + +Device drivers can easily add their own information function for +specific slots (including integrated ones) via the +mca_set_adapter_procfn() call. Drivers that support this are ESDI, IBM +SCSI, and 3c523. If a device is also a module, make sure that the proc +function is removed in the module cleanup. This will require storing +the slot information in a private structure somewhere. See the 3c523 +driver for details. + +Your typical proc function will look something like this: + + static int + dev_getinfo( char* buf, int slot, void* d ) { + struct device* dev = (struct device*) d; + int len = 0; + + len += sprintf( buf+len, "Device: %s\n", dev->name ); + len += sprintf( buf+len, "IRQ: %d\n", dev->irq ); + len += sprintf( buf+len, "IO Port: %#lx-%#lx\n", ... ); + ... + + return len; + } + +Some of the standard MCA information will already be printed, so don't +bother repeating it. Don't try putting in more that 3K of information. + +Enable this function with: + mca_set_adapter_procfn( slot, dev_getinfo, dev ); + +Disable it with: + mca_set_adapter_procfn( slot, NULL, NULL ); + +It is also recommended that, even if you don't write a proc function, to +set the name of the adapter (i.e. "PS/2 ESDI Controller") via +mca_set_adapter_name( int slot, char* name ). Up to 30 characters are +used. + +MCA Device Drivers +================== + +Currently, there are a number of MCA-specific device drivers. + +1) PS/2 ESDI + drivers/block/ps2esdi.c + include/linux/ps2esdi.h + Uses major number 36, and should use /dev files /dev/eda, /dev/edb. + Supports two drives, but only one controller. Usually requires the + command-line args ed=cyl,head,sec + +2) PS/2 SCSI + drivers/scsi/ibmmca.c + drivers/scsi/ibmmca.h + The driver for the IBM SCSI subsystem. Includes both integrated + controllers and adapter cards. May require command-line arg + ibmmcascsi=pun to force detection of an adapter. + +3) 3c523 + drivers/net/3c523.c + drivers/net/3c523.h + 3Com 3c523 Etherlink/MC ethernet driver. + +4) SMC Ultra/MCA + drivers/net/smc-mca.c + drivers/net/smc-mca.h + Elite/A (8013EP/A) and Elite10T/A (8013WP/A) ethernet driver + +As well, drivers/char/psaux.c was modified to support IRQ sharing (it's +#ifdef CONFIG_MCA'ed, for your convenience, although PCI users might be +able to use it...) + +The serial drivers were modified to support the extended IO port range +of the typical MCA system (also #ifdef CONFIG_MCA). + +The following devices work with existing drivers: +1) Token-ring +2) Future Domain SCSI (MCS-600, MCS-700, not MCS-350) +3) Adaptec 1640 SCSI (aha1542 driver) +4) Buslogic SCSI (various) + +Bugs & Other Weirdness +====================== + +NMIs tend to occur with MCA machines because of various hardware +weirdness, bus timeouts, and many other non-critical things. Those of +you who have NMI problems should probably set the CONFIG_IGNORE_NMI flag +somewhere. NMIs seem to be particularly common on the model 70. + +Various Pentium machines have serious problems with the FPU test in +bugs.h. You may need to comment out the FPU test before you can even +boot. This occurs, as far as we know, on the Pentium-equipped 85s, 95s, +and some servers. The PCI/MCA PC 750s are fine as far as I can tell. + +The model 80 has a raft of problems that are just too weird and unique +to get into here. Some people have no trouble while others have nothing +but problems. I'd suspect the problems are related to the age of the +average 80 and accompanying hardware deterioration. + +Credits +======= +A whole pile of people have contributed to the MCA code. I'd include +their names here, but I don't have a list handy. Check the MCA Linux +home page (URL below) for an out-of-date list. + +===================================================================== +http://glycerine.cetmm.uni.edu/mca + +Chris Beauregard +chrisb@truespectra.com |