linux/Documentation/eisa.txt
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   1================
   2EISA bus support
   3================
   4
   5:Author: Marc Zyngier <maz@wild-wind.fr.eu.org>
   6
   7This document groups random notes about porting EISA drivers to the
   8new EISA/sysfs API.
   9
  10Starting from version 2.5.59, the EISA bus is almost given the same
  11status as other much more mainstream busses such as PCI or USB. This
  12has been possible through sysfs, which defines a nice enough set of
  13abstractions to manage busses, devices and drivers.
  14
  15Although the new API is quite simple to use, converting existing
  16drivers to the new infrastructure is not an easy task (mostly because
  17detection code is generally also used to probe ISA cards). Moreover,
  18most EISA drivers are among the oldest Linux drivers so, as you can
  19imagine, some dust has settled here over the years.
  20
  21The EISA infrastructure is made up of three parts:
  22
  23    - The bus code implements most of the generic code. It is shared
  24      among all the architectures that the EISA code runs on. It
  25      implements bus probing (detecting EISA cards available on the bus),
  26      allocates I/O resources, allows fancy naming through sysfs, and
  27      offers interfaces for driver to register.
  28
  29    - The bus root driver implements the glue between the bus hardware
  30      and the generic bus code. It is responsible for discovering the
  31      device implementing the bus, and setting it up to be latter probed
  32      by the bus code. This can go from something as simple as reserving
  33      an I/O region on x86, to the rather more complex, like the hppa
  34      EISA code. This is the part to implement in order to have EISA
  35      running on an "new" platform.
  36
  37    - The driver offers the bus a list of devices that it manages, and
  38      implements the necessary callbacks to probe and release devices
  39      whenever told to.
  40
  41Every function/structure below lives in <linux/eisa.h>, which depends
  42heavily on <linux/device.h>.
  43
  44Bus root driver
  45===============
  46
  47::
  48
  49        int eisa_root_register (struct eisa_root_device *root);
  50
  51The eisa_root_register function is used to declare a device as the
  52root of an EISA bus. The eisa_root_device structure holds a reference
  53to this device, as well as some parameters for probing purposes::
  54
  55        struct eisa_root_device {
  56                struct device   *dev;    /* Pointer to bridge device */
  57                struct resource *res;
  58                unsigned long    bus_base_addr;
  59                int              slots;  /* Max slot number */
  60                int              force_probe; /* Probe even when no slot 0 */
  61                u64              dma_mask; /* from bridge device */
  62                int              bus_nr; /* Set by eisa_root_register */
  63                struct resource  eisa_root_res; /* ditto */
  64        };
  65
  66============= ======================================================
  67node          used for eisa_root_register internal purpose
  68dev           pointer to the root device
  69res           root device I/O resource
  70bus_base_addr slot 0 address on this bus
  71slots         max slot number to probe
  72force_probe   Probe even when slot 0 is empty (no EISA mainboard)
  73dma_mask      Default DMA mask. Usually the bridge device dma_mask.
  74bus_nr        unique bus id, set by eisa_root_register
  75============= ======================================================
  76
  77Driver
  78======
  79
  80::
  81
  82        int eisa_driver_register (struct eisa_driver *edrv);
  83        void eisa_driver_unregister (struct eisa_driver *edrv);
  84
  85Clear enough ?
  86
  87::
  88
  89        struct eisa_device_id {
  90                char sig[EISA_SIG_LEN];
  91                unsigned long driver_data;
  92        };
  93
  94        struct eisa_driver {
  95                const struct eisa_device_id *id_table;
  96                struct device_driver         driver;
  97        };
  98
  99=============== ====================================================
 100id_table        an array of NULL terminated EISA id strings,
 101                followed by an empty string. Each string can
 102                optionally be paired with a driver-dependent value
 103                (driver_data).
 104
 105driver          a generic driver, such as described in
 106                Documentation/driver-model/driver.txt. Only .name,
 107                .probe and .remove members are mandatory.
 108=============== ====================================================
 109
 110An example is the 3c59x driver::
 111
 112        static struct eisa_device_id vortex_eisa_ids[] = {
 113                { "TCM5920", EISA_3C592_OFFSET },
 114                { "TCM5970", EISA_3C597_OFFSET },
 115                { "" }
 116        };
 117
 118        static struct eisa_driver vortex_eisa_driver = {
 119                .id_table = vortex_eisa_ids,
 120                .driver   = {
 121                        .name    = "3c59x",
 122                        .probe   = vortex_eisa_probe,
 123                        .remove  = vortex_eisa_remove
 124                }
 125        };
 126
 127Device
 128======
 129
 130The sysfs framework calls .probe and .remove functions upon device
 131discovery and removal (note that the .remove function is only called
 132when driver is built as a module).
 133
 134Both functions are passed a pointer to a 'struct device', which is
 135encapsulated in a 'struct eisa_device' described as follows::
 136
 137        struct eisa_device {
 138                struct eisa_device_id id;
 139                int                   slot;
 140                int                   state;
 141                unsigned long         base_addr;
 142                struct resource       res[EISA_MAX_RESOURCES];
 143                u64                   dma_mask;
 144                struct device         dev; /* generic device */
 145        };
 146
 147======== ============================================================
 148id       EISA id, as read from device. id.driver_data is set from the
 149         matching driver EISA id.
 150slot     slot number which the device was detected on
 151state    set of flags indicating the state of the device. Current
 152         flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
 153res      set of four 256 bytes I/O regions allocated to this device
 154dma_mask DMA mask set from the parent device.
 155dev      generic device (see Documentation/driver-model/device.txt)
 156======== ============================================================
 157
 158You can get the 'struct eisa_device' from 'struct device' using the
 159'to_eisa_device' macro.
 160
 161Misc stuff
 162==========
 163
 164::
 165
 166        void eisa_set_drvdata (struct eisa_device *edev, void *data);
 167
 168Stores data into the device's driver_data area.
 169
 170::
 171
 172        void *eisa_get_drvdata (struct eisa_device *edev):
 173
 174Gets the pointer previously stored into the device's driver_data area.
 175
 176::
 177
 178        int eisa_get_region_index (void *addr);
 179
 180Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
 181address.
 182
 183Kernel parameters
 184=================
 185
 186eisa_bus.enable_dev
 187        A comma-separated list of slots to be enabled, even if the firmware
 188        set the card as disabled. The driver must be able to properly
 189        initialize the device in such conditions.
 190
 191eisa_bus.disable_dev
 192        A comma-separated list of slots to be enabled, even if the firmware
 193        set the card as enabled. The driver won't be called to handle this
 194        device.
 195
 196virtual_root.force_probe
 197        Force the probing code to probe EISA slots even when it cannot find an
 198        EISA compliant mainboard (nothing appears on slot 0). Defaults to 0
 199        (don't force), and set to 1 (force probing) when either
 200        CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set.
 201
 202Random notes
 203============
 204
 205Converting an EISA driver to the new API mostly involves *deleting*
 206code (since probing is now in the core EISA code). Unfortunately, most
 207drivers share their probing routine between ISA, and EISA. Special
 208care must be taken when ripping out the EISA code, so other busses
 209won't suffer from these surgical strikes...
 210
 211You *must not* expect any EISA device to be detected when returning
 212from eisa_driver_register, since the chances are that the bus has not
 213yet been probed. In fact, that's what happens most of the time (the
 214bus root driver usually kicks in rather late in the boot process).
 215Unfortunately, most drivers are doing the probing by themselves, and
 216expect to have explored the whole machine when they exit their probe
 217routine.
 218
 219For example, switching your favorite EISA SCSI card to the "hotplug"
 220model is "the right thing"(tm).
 221
 222Thanks
 223======
 224
 225I'd like to thank the following people for their help:
 226
 227- Xavier Benigni for lending me a wonderful Alpha Jensen,
 228- James Bottomley, Jeff Garzik for getting this stuff into the kernel,
 229- Andries Brouwer for contributing numerous EISA ids,
 230- Catrin Jones for coping with far too many machines at home.
 231