path: root/Documentation/eisa.txt
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/eisa.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+EISA bus support (Marc Zyngier <maz@wild-wind.fr.eu.org>)
+This document groups random notes about porting EISA drivers to the
+new EISA/sysfs API.
+Starting from version 2.5.59, the EISA bus is almost given the same
+status as other much more mainstream busses such as PCI or USB. This
+has been possible through sysfs, which defines a nice enough set of
+abstractions to manage busses, devices and drivers.
+Although the new API is quite simple to use, converting existing
+drivers to the new infrastructure is not an easy task (mostly because
+detection code is generally also used to probe ISA cards). Moreover,
+most EISA drivers are among the oldest Linux drivers so, as you can
+imagine, some dust has settled here over the years.
+The EISA infrastructure is made up of three parts :
+ - The bus code implements most of the generic code. It is shared
+ among all the architectures that the EISA code runs on. It
+ implements bus probing (detecting EISA cards avaible on the bus),
+ allocates I/O resources, allows fancy naming through sysfs, and
+ offers interfaces for driver to register.
+ - The bus root driver implements the glue between the bus hardware
+ and the generic bus code. It is responsible for discovering the
+ device implementing the bus, and setting it up to be latter probed
+ by the bus code. This can go from something as simple as reserving
+ an I/O region on x86, to the rather more complex, like the hppa
+ EISA code. This is the part to implement in order to have EISA
+ running on an "new" platform.
+ - The driver offers the bus a list of devices that it manages, and
+ implements the necessary callbacks to probe and release devices
+ whenever told to.
+Every function/structure below lives in <linux/eisa.h>, which depends
+heavily on <linux/device.h>.
+** Bus root driver :
+int eisa_root_register (struct eisa_root_device *root);
+The eisa_root_register function is used to declare a device as the
+root of an EISA bus. The eisa_root_device structure holds a reference
+to this device, as well as some parameters for probing purposes.
+struct eisa_root_device {
+ struct device *dev; /* Pointer to bridge device */
+ struct resource *res;
+ unsigned long bus_base_addr;
+ int slots; /* Max slot number */
+ int force_probe; /* Probe even when no slot 0 */
+ u64 dma_mask; /* from bridge device */
+ int bus_nr; /* Set by eisa_root_register */
+ struct resource eisa_root_res; /* ditto */
+node : used for eisa_root_register internal purpose
+dev : pointer to the root device
+res : root device I/O resource
+bus_base_addr : slot 0 address on this bus
+slots : max slot number to probe
+force_probe : Probe even when slot 0 is empty (no EISA mainboard)
+dma_mask : Default DMA mask. Usualy the bridge device dma_mask.
+bus_nr : unique bus id, set by eisa_root_register
+** Driver :
+int eisa_driver_register (struct eisa_driver *edrv);
+void eisa_driver_unregister (struct eisa_driver *edrv);
+Clear enough ?
+struct eisa_device_id {
+ char sig[EISA_SIG_LEN];
+ unsigned long driver_data;
+struct eisa_driver {
+ const struct eisa_device_id *id_table;
+ struct device_driver driver;
+id_table : an array of NULL terminated EISA id strings,
+ followed by an empty string. Each string can
+ optionnaly be paired with a driver-dependant value
+ (driver_data).
+driver : a generic driver, such as described in
+ Documentation/driver-model/driver.txt. Only .name,
+ .probe and .remove members are mandatory.
+An example is the 3c59x driver :
+static struct eisa_device_id vortex_eisa_ids[] = {
+ { "TCM5920", EISA_3C592_OFFSET },
+ { "TCM5970", EISA_3C597_OFFSET },
+ { "" }
+static struct eisa_driver vortex_eisa_driver = {
+ .id_table = vortex_eisa_ids,
+ .driver = {
+ .name = "3c59x",
+ .probe = vortex_eisa_probe,
+ .remove = vortex_eisa_remove
+ }
+** Device :
+The sysfs framework calls .probe and .remove functions upon device
+discovery and removal (note that the .remove function is only called
+when driver is built as a module).
+Both functions are passed a pointer to a 'struct device', which is
+encapsulated in a 'struct eisa_device' described as follows :
+struct eisa_device {
+ struct eisa_device_id id;
+ int slot;
+ int state;
+ unsigned long base_addr;
+ struct resource res[EISA_MAX_RESOURCES];
+ u64 dma_mask;
+ struct device dev; /* generic device */
+id : EISA id, as read from device. id.driver_data is set from the
+ matching driver EISA id.
+slot : slot number which the device was detected on
+state : set of flags indicating the state of the device. Current
+res : set of four 256 bytes I/O regions allocated to this device
+dma_mask: DMA mask set from the parent device.
+dev : generic device (see Documentation/driver-model/device.txt)
+You can get the 'struct eisa_device' from 'struct device' using the
+'to_eisa_device' macro.
+** Misc stuff :
+void eisa_set_drvdata (struct eisa_device *edev, void *data);
+Stores data into the device's driver_data area.
+void *eisa_get_drvdata (struct eisa_device *edev):
+Gets the pointer previously stored into the device's driver_data area.
+int eisa_get_region_index (void *addr);
+Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
+** Kernel parameters :
+eisa_bus.enable_dev :
+A comma-separated list of slots to be enabled, even if the firmware
+set the card as disabled. The driver must be able to properly
+initialize the device in such conditions.
+eisa_bus.disable_dev :
+A comma-separated list of slots to be enabled, even if the firmware
+set the card as enabled. The driver won't be called to handle this
+virtual_root.force_probe :
+Force the probing code to probe EISA slots even when it cannot find an
+EISA compliant mainboard (nothing appears on slot 0). Defaultd to 0
+(don't force), and set to 1 (force probing) when either
+** Random notes :
+Converting an EISA driver to the new API mostly involves *deleting*
+code (since probing is now in the core EISA code). Unfortunately, most
+drivers share their probing routine between ISA, MCA and EISA. Special
+care must be taken when ripping out the EISA code, so other busses
+won't suffer from these surgical strikes...
+You *must not* expect any EISA device to be detected when returning
+from eisa_driver_register, since the chances are that the bus has not
+yet been probed. In fact, that's what happens most of the time (the
+bus root driver usually kicks in rather late in the boot process).
+Unfortunately, most drivers are doing the probing by themselves, and
+expect to have explored the whole machine when they exit their probe
+For example, switching your favorite EISA SCSI card to the "hotplug"
+model is "the right thing"(tm).
+** Thanks :
+I'd like to thank the following people for their help :
+- Xavier Benigni for lending me a wonderful Alpha Jensen,
+- James Bottomley, Jeff Garzik for getting this stuff into the kernel,
+- Andries Brouwer for contributing numerous EISA ids,
+- Catrin Jones for coping with far too many machines at home.