linux/Documentation/eisa.txt
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   1EISA bus support (Marc Zyngier <maz@wild-wind.fr.eu.org>)
   2
   3This document groups random notes about porting EISA drivers to the
   4new EISA/sysfs API.
   5
   6Starting from version 2.5.59, the EISA bus is almost given the same
   7status as other much more mainstream busses such as PCI or USB. This
   8has been possible through sysfs, which defines a nice enough set of
   9abstractions to manage busses, devices and drivers.
  10
  11Although the new API is quite simple to use, converting existing
  12drivers to the new infrastructure is not an easy task (mostly because
  13detection code is generally also used to probe ISA cards). Moreover,
  14most EISA drivers are among the oldest Linux drivers so, as you can
  15imagine, some dust has settled here over the years.
  16
  17The EISA infrastructure is made up of three parts :
  18
  19    - The bus code implements most of the generic code. It is shared
  20    among all the architectures that the EISA code runs on. It
  21    implements bus probing (detecting EISA cards available on the bus),
  22    allocates I/O resources, allows fancy naming through sysfs, and
  23    offers interfaces for driver to register.
  24
  25    - The bus root driver implements the glue between the bus hardware
  26    and the generic bus code. It is responsible for discovering the
  27    device implementing the bus, and setting it up to be latter probed
  28    by the bus code. This can go from something as simple as reserving
  29    an I/O region on x86, to the rather more complex, like the hppa
  30    EISA code. This is the part to implement in order to have EISA
  31    running on an "new" platform.
  32
  33    - The driver offers the bus a list of devices that it manages, and
  34    implements the necessary callbacks to probe and release devices
  35    whenever told to.
  36
  37Every function/structure below lives in <linux/eisa.h>, which depends
  38heavily on <linux/device.h>.
  39
  40** Bus root driver :
  41
  42int eisa_root_register (struct eisa_root_device *root);
  43
  44The eisa_root_register function is used to declare a device as the
  45root of an EISA bus. The eisa_root_device structure holds a reference
  46to this device, as well as some parameters for probing purposes.
  47
  48struct eisa_root_device {
  49        struct device   *dev;    /* Pointer to bridge device */
  50        struct resource *res;
  51        unsigned long    bus_base_addr;
  52        int              slots;  /* Max slot number */
  53        int              force_probe; /* Probe even when no slot 0 */
  54        u64              dma_mask; /* from bridge device */
  55        int              bus_nr; /* Set by eisa_root_register */
  56        struct resource  eisa_root_res; /* ditto */
  57};
  58
  59node          : used for eisa_root_register internal purpose
  60dev           : pointer to the root device
  61res           : root device I/O resource
  62bus_base_addr : slot 0 address on this bus
  63slots         : max slot number to probe
  64force_probe   : Probe even when slot 0 is empty (no EISA mainboard)
  65dma_mask      : Default DMA mask. Usually the bridge device dma_mask.
  66bus_nr        : unique bus id, set by eisa_root_register
  67
  68** Driver :
  69
  70int eisa_driver_register (struct eisa_driver *edrv);
  71void eisa_driver_unregister (struct eisa_driver *edrv);
  72
  73Clear enough ?
  74
  75struct eisa_device_id {
  76        char sig[EISA_SIG_LEN];
  77        unsigned long driver_data;
  78};
  79
  80struct eisa_driver {
  81        const struct eisa_device_id *id_table;
  82        struct device_driver         driver;
  83};
  84
  85id_table        : an array of NULL terminated EISA id strings,
  86                  followed by an empty string. Each string can
  87                  optionally be paired with a driver-dependent value
  88                  (driver_data).
  89
  90driver          : a generic driver, such as described in
  91                  Documentation/driver-model/driver.txt. Only .name,
  92                  .probe and .remove members are mandatory.
  93
  94An example is the 3c59x driver :
  95
  96static struct eisa_device_id vortex_eisa_ids[] = {
  97        { "TCM5920", EISA_3C592_OFFSET },
  98        { "TCM5970", EISA_3C597_OFFSET },
  99        { "" }
 100};
 101
 102static struct eisa_driver vortex_eisa_driver = {
 103        .id_table = vortex_eisa_ids,
 104        .driver   = {
 105                .name    = "3c59x",
 106                .probe   = vortex_eisa_probe,
 107                .remove  = vortex_eisa_remove
 108        }
 109};
 110
 111** Device :
 112
 113The sysfs framework calls .probe and .remove functions upon device
 114discovery and removal (note that the .remove function is only called
 115when driver is built as a module).
 116
 117Both functions are passed a pointer to a 'struct device', which is
 118encapsulated in a 'struct eisa_device' described as follows :
 119
 120struct eisa_device {
 121        struct eisa_device_id id;
 122        int                   slot;
 123        int                   state;
 124        unsigned long         base_addr;
 125        struct resource       res[EISA_MAX_RESOURCES];
 126        u64                   dma_mask;
 127        struct device         dev; /* generic device */
 128};
 129
 130id      : EISA id, as read from device. id.driver_data is set from the
 131          matching driver EISA id.
 132slot    : slot number which the device was detected on
 133state   : set of flags indicating the state of the device. Current
 134          flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
 135res     : set of four 256 bytes I/O regions allocated to this device
 136dma_mask: DMA mask set from the parent device.
 137dev     : generic device (see Documentation/driver-model/device.txt)
 138
 139You can get the 'struct eisa_device' from 'struct device' using the
 140'to_eisa_device' macro.
 141
 142** Misc stuff :
 143
 144void eisa_set_drvdata (struct eisa_device *edev, void *data);
 145
 146Stores data into the device's driver_data area.
 147
 148void *eisa_get_drvdata (struct eisa_device *edev):
 149
 150Gets the pointer previously stored into the device's driver_data area.
 151
 152int eisa_get_region_index (void *addr);
 153
 154Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
 155address.
 156
 157** Kernel parameters :
 158
 159eisa_bus.enable_dev :
 160
 161A comma-separated list of slots to be enabled, even if the firmware
 162set the card as disabled. The driver must be able to properly
 163initialize the device in such conditions.
 164
 165eisa_bus.disable_dev :
 166
 167A comma-separated list of slots to be enabled, even if the firmware
 168set the card as enabled. The driver won't be called to handle this
 169device.
 170
 171virtual_root.force_probe :
 172
 173Force the probing code to probe EISA slots even when it cannot find an
 174EISA compliant mainboard (nothing appears on slot 0). Defaults to 0
 175(don't force), and set to 1 (force probing) when either
 176CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set.
 177
 178** Random notes :
 179
 180Converting an EISA driver to the new API mostly involves *deleting*
 181code (since probing is now in the core EISA code). Unfortunately, most
 182drivers share their probing routine between ISA, and EISA. Special
 183care must be taken when ripping out the EISA code, so other busses
 184won't suffer from these surgical strikes...
 185
 186You *must not* expect any EISA device to be detected when returning
 187from eisa_driver_register, since the chances are that the bus has not
 188yet been probed. In fact, that's what happens most of the time (the
 189bus root driver usually kicks in rather late in the boot process).
 190Unfortunately, most drivers are doing the probing by themselves, and
 191expect to have explored the whole machine when they exit their probe
 192routine.
 193
 194For example, switching your favorite EISA SCSI card to the "hotplug"
 195model is "the right thing"(tm).
 196
 197** Thanks :
 198
 199I'd like to thank the following people for their help :
 200- Xavier Benigni for lending me a wonderful Alpha Jensen,
 201- James Bottomley, Jeff Garzik for getting this stuff into the kernel,
 202- Andries Brouwer for contributing numerous EISA ids,
 203- Catrin Jones for coping with far too many machines at home.
 204
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