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-api/driver-model/driver.rst. 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-api/driver-model/device.rst)
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 disabled, 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
200 CONFIG_EISA_VLB_PRIMING is 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.
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