231 lines
7.6 KiB
ReStructuredText
231 lines
7.6 KiB
ReStructuredText
================
|
|
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-api/driver-model/driver.rst. 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-api/driver-model/device.rst)
|
|
======== ============================================================
|
|
|
|
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.
|