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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

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.
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