patch-2.1.15 linux/Documentation/mca.txt

• Lines: 211
• Date: Thu Dec 12 16:51:07 1996
• Orig file: v2.1.14/linux/Documentation/mca.txt
• Orig date: Thu Jan 1 02:00:00 1970

diff -u --recursive --new-file v2.1.14/linux/Documentation/mca.txt linux/Documentation/mca.txt
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+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