Documentation/eisa.txt

   1 ================
   2 EISA bus support
   3 ================
   4
   5 :Author: Marc Zyngier <maz@wild-wind.fr.eu.org>
   6
   7 This document groups random notes about porting EISA drivers to the
   8 new EISA/sysfs API.
   9
  10 Starting from version 2.5.59, the EISA bus is almost given the same
  11 status as other much more mainstream busses such as PCI or USB. This
  12 has been possible through sysfs, which defines a nice enough set of
  13 abstractions to manage busses, devices and drivers.
  14
  15 Although the new API is quite simple to use, converting existing
  16 drivers to the new infrastructure is not an easy task (mostly because
  17 detection code is generally also used to probe ISA cards). Moreover,
  18 most EISA drivers are among the oldest Linux drivers so, as you can
  19 imagine, some dust has settled here over the years.
  20
  21 The 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
  41 Every function/structure below lives in <linux/eisa.h>, which depends
  42 heavily on <linux/device.h>.
  43
  44 Bus root driver
  45 ===============
  46
  47 ::
  48
  49         int eisa_root_register (struct eisa_root_device *root);
  50
  51 The eisa_root_register function is used to declare a device as the
  52 root of an EISA bus. The eisa_root_device structure holds a reference
  53 to 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 ============= ======================================================
  67 node          used for eisa_root_register internal purpose
  68 dev           pointer to the root device
  69 res           root device I/O resource
  70 bus_base_addr slot 0 address on this bus
  71 slots         max slot number to probe
  72 force_probe   Probe even when slot 0 is empty (no EISA mainboard)
  73 dma_mask      Default DMA mask. Usually the bridge device dma_mask.
  74 bus_nr        unique bus id, set by eisa_root_register
  75 ============= ======================================================
  76
  77 Driver
  78 ======
  79
  80 ::
  81
  82         int eisa_driver_register (struct eisa_driver *edrv);
  83         void eisa_driver_unregister (struct eisa_driver *edrv);
  84
  85 Clear 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 =============== ====================================================
 100 id_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
 105 driver          a generic driver, such as described in
 106                 Documentation/driver-model/driver.txt. Only .name,
 107                 .probe and .remove members are mandatory.
 108 =============== ====================================================
 109
 110 An 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
 127 Device
 128 ======
 129
 130 The sysfs framework calls .probe and .remove functions upon device
 131 discovery and removal (note that the .remove function is only called
 132 when driver is built as a module).
 133
 134 Both functions are passed a pointer to a 'struct device', which is
 135 encapsulated 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 ======== ============================================================
 148 id       EISA id, as read from device. id.driver_data is set from the
 149          matching driver EISA id.
 150 slot     slot number which the device was detected on
 151 state    set of flags indicating the state of the device. Current
 152          flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
 153 res      set of four 256 bytes I/O regions allocated to this device
 154 dma_mask DMA mask set from the parent device.
 155 dev      generic device (see Documentation/driver-model/device.txt)
 156 ======== ============================================================
 157
 158 You can get the 'struct eisa_device' from 'struct device' using the
 159 'to_eisa_device' macro.
 160
 161 Misc stuff
 162 ==========
 163
 164 ::
 165
 166         void eisa_set_drvdata (struct eisa_device *edev, void *data);
 167
 168 Stores data into the device's driver_data area.
 169
 170 ::
 171
 172         void *eisa_get_drvdata (struct eisa_device *edev):
 173
 174 Gets the pointer previously stored into the device's driver_data area.
 175
 176 ::
 177
 178         int eisa_get_region_index (void *addr);
 179
 180 Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
 181 address.
 182
 183 Kernel parameters
 184 =================
 185
 186 eisa_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
 191 eisa_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
 196 virtual_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
 202 Random notes
 203 ============
 204
 205 Converting an EISA driver to the new API mostly involves *deleting*
 206 code (since probing is now in the core EISA code). Unfortunately, most
 207 drivers share their probing routine between ISA, and EISA. Special
 208 care must be taken when ripping out the EISA code, so other busses
 209 won't suffer from these surgical strikes...
 210
 211 You *must not* expect any EISA device to be detected when returning
 212 from eisa_driver_register, since the chances are that the bus has not
 213 yet been probed. In fact, that's what happens most of the time (the
 214 bus root driver usually kicks in rather late in the boot process).
 215 Unfortunately, most drivers are doing the probing by themselves, and
 216 expect to have explored the whole machine when they exit their probe
 217 routine.
 218
 219 For example, switching your favorite EISA SCSI card to the "hotplug"
 220 model is "the right thing"(tm).
 221
 222 Thanks
 223 ======
 224
 225 I'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.