FreeBSD/Linux Kernel Cross Reference
sys/Documentation/mca.txt

     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/x86/kernel/mca_32.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/x86/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 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.
   
   2) 3c523
           drivers/net/3c523.c
           drivers/net/3c523.h
      3Com 3c523 Etherlink/MC ethernet driver.
   
   3) 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).
   
   4) 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.
   
   5) Future Domain MCS-600/700, OEM'd IBM Fast SCSI Adapter/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://www.dgmicro.com/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

Cache object: 470037acce9ffc42a3d22861d2c66ab0