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diff --git a/Documentation/eisa.txt b/Documentation/eisa.txt new file mode 100644 index 000000000..2806e5544 --- /dev/null +++ b/Documentation/eisa.txt @@ -0,0 +1,230 @@ +================ +EISA bus support +================ + +:Author: 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 available 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. Usually 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 + optionally be paired with a driver-dependent 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 + flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED. +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 +address. + +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 + device. + +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). Defaults to 0 + (don't force), and set to 1 (force probing) when either + CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set. + +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, 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 +routine. + +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. |