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Linux/Documentation/eisa.txt

  1 EISA bus support (Marc Zyngier <maz@wild-wind.fr.eu.org>)
  2 
  3 This document groups random notes about porting EISA drivers to the
  4 new EISA/sysfs API.
  5 
  6 Starting from version 2.5.59, the EISA bus is almost given the same
  7 status as other much more mainstream busses such as PCI or USB. This
  8 has been possible through sysfs, which defines a nice enough set of
  9 abstractions to manage busses, devices and drivers.
 10 
 11 Although the new API is quite simple to use, converting existing
 12 drivers to the new infrastructure is not an easy task (mostly because
 13 detection code is generally also used to probe ISA cards). Moreover,
 14 most EISA drivers are among the oldest Linux drivers so, as you can
 15 imagine, some dust has settled here over the years.
 16 
 17 The 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 
 37 Every function/structure below lives in <linux/eisa.h>, which depends
 38 heavily on <linux/device.h>.
 39 
 40 ** Bus root driver :
 41 
 42 int eisa_root_register (struct eisa_root_device *root);
 43 
 44 The eisa_root_register function is used to declare a device as the
 45 root of an EISA bus. The eisa_root_device structure holds a reference
 46 to this device, as well as some parameters for probing purposes.
 47 
 48 struct 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 
 59 node          : used for eisa_root_register internal purpose
 60 dev           : pointer to the root device
 61 res           : root device I/O resource
 62 bus_base_addr : slot 0 address on this bus
 63 slots         : max slot number to probe
 64 force_probe   : Probe even when slot 0 is empty (no EISA mainboard)
 65 dma_mask      : Default DMA mask. Usually the bridge device dma_mask.
 66 bus_nr        : unique bus id, set by eisa_root_register
 67 
 68 ** Driver :
 69 
 70 int eisa_driver_register (struct eisa_driver *edrv);
 71 void eisa_driver_unregister (struct eisa_driver *edrv);
 72 
 73 Clear enough ?
 74 
 75 struct eisa_device_id {
 76         char sig[EISA_SIG_LEN];
 77         unsigned long driver_data;
 78 };
 79 
 80 struct eisa_driver {
 81         const struct eisa_device_id *id_table;
 82         struct device_driver         driver;
 83 };
 84 
 85 id_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 
 90 driver          : a generic driver, such as described in
 91                   Documentation/driver-model/driver.txt. Only .name,
 92                   .probe and .remove members are mandatory.
 93 
 94 An example is the 3c59x driver :
 95 
 96 static struct eisa_device_id vortex_eisa_ids[] = {
 97         { "TCM5920", EISA_3C592_OFFSET },
 98         { "TCM5970", EISA_3C597_OFFSET },
 99         { "" }
100 };
101 
102 static 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 
113 The sysfs framework calls .probe and .remove functions upon device
114 discovery and removal (note that the .remove function is only called
115 when driver is built as a module).
116 
117 Both functions are passed a pointer to a 'struct device', which is
118 encapsulated in a 'struct eisa_device' described as follows :
119 
120 struct 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 
130 id      : EISA id, as read from device. id.driver_data is set from the
131           matching driver EISA id.
132 slot    : slot number which the device was detected on
133 state   : set of flags indicating the state of the device. Current
134           flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
135 res     : set of four 256 bytes I/O regions allocated to this device
136 dma_mask: DMA mask set from the parent device.
137 dev     : generic device (see Documentation/driver-model/device.txt)
138 
139 You can get the 'struct eisa_device' from 'struct device' using the
140 'to_eisa_device' macro.
141 
142 ** Misc stuff :
143 
144 void eisa_set_drvdata (struct eisa_device *edev, void *data);
145 
146 Stores data into the device's driver_data area.
147 
148 void *eisa_get_drvdata (struct eisa_device *edev):
149 
150 Gets the pointer previously stored into the device's driver_data area.
151 
152 int eisa_get_region_index (void *addr);
153 
154 Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
155 address.
156 
157 ** Kernel parameters :
158 
159 eisa_bus.enable_dev :
160 
161 A comma-separated list of slots to be enabled, even if the firmware
162 set the card as disabled. The driver must be able to properly
163 initialize the device in such conditions.
164 
165 eisa_bus.disable_dev :
166 
167 A comma-separated list of slots to be enabled, even if the firmware
168 set the card as enabled. The driver won't be called to handle this
169 device.
170 
171 virtual_root.force_probe :
172 
173 Force the probing code to probe EISA slots even when it cannot find an
174 EISA compliant mainboard (nothing appears on slot 0). Defaults to 0
175 (don't force), and set to 1 (force probing) when either
176 CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set.
177 
178 ** Random notes :
179 
180 Converting an EISA driver to the new API mostly involves *deleting*
181 code (since probing is now in the core EISA code). Unfortunately, most
182 drivers share their probing routine between ISA, and EISA. Special
183 care must be taken when ripping out the EISA code, so other busses
184 won't suffer from these surgical strikes...
185 
186 You *must not* expect any EISA device to be detected when returning
187 from eisa_driver_register, since the chances are that the bus has not
188 yet been probed. In fact, that's what happens most of the time (the
189 bus root driver usually kicks in rather late in the boot process).
190 Unfortunately, most drivers are doing the probing by themselves, and
191 expect to have explored the whole machine when they exit their probe
192 routine.
193 
194 For example, switching your favorite EISA SCSI card to the "hotplug"
195 model is "the right thing"(tm).
196 
197 ** Thanks :
198 
199 I'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.

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