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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 net_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 use 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 (actually, smc-mca.c has a slightly more complex example that can
+handle a list of adapter ids).
+
+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 blindness.
+
+User level drivers (such as the AGX X server) can use /proc/mca/pos 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
+=========
+
+/proc/mca is 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
+
+See Appendix A for a sample.
+
+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 net_device* dev = (struct net_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 than 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 ).
+
+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.  May use the
+   command-line args "ed=cyl,head,sec" and "tp720".
+
+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=io_port" to force detection of an adapter.  If you have a
+   machine with a front-panel display (i.e. model 95), you can use
+   "ibmmcascsi=display" to enable a drive activity indicator.
+
+3) 3c523
+        drivers/net/3c523.c
+        drivers/net/3c523.h
+   3Com 3c523 Etherlink/MC ethernet driver.
+
+4) SMC Ultra/MCA and IBM Adapter/A
+        drivers/net/smc-mca.c
+        drivers/net/smc-mca.h
+        Driver for the MCA version of the SMC Ultra and various other
+        OEM'ed and work-alike cards (Elite, Adapter/A, etc).
+
+5) NE/2
+        driver/net/ne2.c
+        driver/net/ne2.h
+        The NE/2 is the MCA version of the NE2000.  This may not work
+        with clones that have a different adapter id than the original
+        NE/2.
+
+6) Future Domain MCS-600/700, OEM'd IBM Fast SCSI Aapter/A and
+   Reply Sound Blaster/SCSI (SCSI part)
+        Better support for these cards than the driver for ISA.
+   Supports multiple cards with IRQ sharing.
+
+Also added boot time option of scsi-probe, which can do reordering of
+SCSI host adapters. This will direct the kernel on the order which
+SCSI adapter should be detected. Example:
+  scsi-probe=ibmmca,fd_mcs,adaptec1542,buslogic
+
+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, OEM'ed IBM SCSI)
+3) Adaptec 1640 SCSI (using the aha1542 driver)
+4) Bustek/Buslogic SCSI (various)
+5) Probably all Arcnet cards.
+6) Some, possibly all, MCA IDE controllers.
+7) 3Com 3c529 (MCA version of 3c509) (patched)
+
+8) Intel EtherExpressMC  (patched version)
+   You need to have CONFIG_MCA defined to have EtherExpressMC support.
+9) Reply Sound Blaster/SCSI (SB part) (patched version)
+
+Bugs & Other Weirdness
+======================
+
+NMIs tend to occur with MCA machines because of various hardware
+weirdness, bus timeouts, and many other non-critical things.  Some basic
+code to handle them (inspired by the NetBSD MCA code) has been added to
+detect the guilty device, but it's pretty incomplete.  If NMIs are a
+persistent problem (on some model 70 or 80s, they occur every couple
+shell commands), the CONFIG_IGNORE_NMI flag will take care of that.
+
+Various Pentium machines have had serious problems with the FPU test in
+bugs.h.  Basically, the machine hangs after the HLT test.  This occurs,
+as far as we know, on the Pentium-equipped 85s, 95s, and some PC Servers.
+The PCI/MCA PC 750s are fine as far as I can tell.  The ``mca-pentium''
+boot-prompt flag will disable the FPU bug check if this is a problem
+with your machine.
+
+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 some problems are related to the age of the
+average 80 and accompanying hardware deterioration, although others
+are definitely design problems with the hardware.  Among the problems
+include SCSI controller problems, ESDI controller problems, and serious
+screw-ups in the floppy controller.  Oh, and the parallel port is also
+pretty flaky.  There were about 5 or 6 different model 80 motherboards
+produced to fix various obscure problems.  As far as I know, it's pretty
+much impossible to tell which bugs a particular model 80 has (other than
+triggering them, that is).
+
+Drivers are required for some MCA memory adapters.  If you're suddenly
+short a few megs of RAM, this might be the reason.  The (I think) Enhanced
+Memory Adapter commonly found on the model 70 is one.  There's a very
+alpha driver floating around, but it's pretty ugly (disassembled from
+the DOS driver, actually).  See the MCA Linux web page (URL below)
+for more current memory info.
+
+The Thinkpad 700 and 720 will work, but various components are either
+non-functional, flaky, or we don't know anything about them.  The
+graphics controller is supposed to be some WD, but we can't get things
+working properly.  The PCMCIA slots don't seem to work.  Ditto for APM.
+The serial ports work, but detection seems to be flaky.
+
+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 a perpetually out-of-date list.
+
+=====================================================================
+MCA Linux Home Page: http://glycerine.itsmm.uni.edu/mca/
+
+Christophe Beauregard
+chrisb@truespectra.com
+cpbeaure@calum.csclub.uwaterloo.ca
+
+=====================================================================
+Appendix A: Sample /proc/mca
+
+This is from my model 8595.  Slot 1 contains the standard IBM SCSI
+adapter, slot 3 is an Adaptec AHA-1640, slot 5 is a XGA-1 video adapter,
+and slot 7 is the 3c523 Etherlink/MC.
+
+/proc/mca/machine:
+Model Id: 0xf8
+Submodel Id: 0x14
+BIOS Revision: 0x5
+
+/proc/mca/pos:
+Slot 1: ff 8e f1 fc a0 ff ff ff  IBM SCSI Adapter w/Cache
+Slot 2: ff ff ff ff ff ff ff ff  
+Slot 3: 1f 0f 81 3b bf b6 ff ff  
+Slot 4: ff ff ff ff ff ff ff ff  
+Slot 5: db 8f 1d 5e fd c0 00 00  
+Slot 6: ff ff ff ff ff ff ff ff  
+Slot 7: 42 60 ff 08 ff ff ff ff  3Com 3c523 Etherlink/MC
+Slot 8: ff ff ff ff ff ff ff ff  
+Video : ff ff ff ff ff ff ff ff  
+SCSI  : ff ff ff ff ff ff ff ff  
+
+/proc/mca/slot1:
+Slot: 1
+Adapter Name: IBM SCSI Adapter w/Cache
+Id: 8eff
+Enabled: Yes
+POS: ff 8e f1 fc a0 ff ff ff 
+Subsystem PUN: 7
+Detected at boot: Yes
+
+/proc/mca/slot3:
+Slot: 3
+Adapter Name: Unknown
+Id: 0f1f
+Enabled: Yes
+POS: 1f 0f 81 3b bf b6 ff ff 
+
+/proc/mca/slot5:
+Slot: 5
+Adapter Name: Unknown
+Id: 8fdb
+Enabled: Yes
+POS: db 8f 1d 5e fd c0 00 00 
+
+/proc/mca/slot7:
+Slot: 7
+Adapter Name: 3Com 3c523 Etherlink/MC
+Id: 6042
+Enabled: Yes
+POS: 42 60 ff 08 ff ff ff ff 
+Revision: 0xe
+IRQ: 9
+IO Address: 0x3300-0x3308
+Memory: 0xd8000-0xdbfff
+Transceiver: External
+Device: eth0
+Hardware Address: 02 60 8c 45 c4 2a