Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 EISA bus support (Marc Zyngier <maz[AT]wild-wind.fr.eu[DOT]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-dependant 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). Defaultd 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, MCA 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.
