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| -rw-r--r-- | Documentation/isa.txt | 121 | ||||
| -rw-r--r-- | MAINTAINERS | 7 |
2 files changed, 128 insertions, 0 deletions
diff --git a/Documentation/isa.txt b/Documentation/isa.txt new file mode 100644 index 000000000000..f232c26a40be --- /dev/null +++ b/Documentation/isa.txt @@ -0,0 +1,121 @@ +ISA Drivers +----------- + +The following text is adapted from the commit message of the initial +commit of the ISA bus driver authored by Rene Herman. + +During the recent "isa drivers using platform devices" discussion it was +pointed out that (ALSA) ISA drivers ran into the problem of not having +the option to fail driver load (device registration rather) upon not +finding their hardware due to a probe() error not being passed up +through the driver model. In the course of that, I suggested a separate +ISA bus might be best; Russell King agreed and suggested this bus could +use the .match() method for the actual device discovery. + +The attached does this. For this old non (generically) discoverable ISA +hardware only the driver itself can do discovery so as a difference with +the platform_bus, this isa_bus also distributes match() up to the +driver. + +As another difference: these devices only exist in the driver model due +to the driver creating them because it might want to drive them, meaning +that all device creation has been made internal as well. + +The usage model this provides is nice, and has been acked from the ALSA +side by Takashi Iwai and Jaroslav Kysela. The ALSA driver module_init's +now (for oldisa-only drivers) become: + +static int __init alsa_card_foo_init(void) +{ + return isa_register_driver(&snd_foo_isa_driver, SNDRV_CARDS); +} + +static void __exit alsa_card_foo_exit(void) +{ + isa_unregister_driver(&snd_foo_isa_driver); +} + +Quite like the other bus models therefore. This removes a lot of +duplicated init code from the ALSA ISA drivers. + +The passed in isa_driver struct is the regular driver struct embedding a +struct device_driver, the normal probe/remove/shutdown/suspend/resume +callbacks, and as indicated that .match callback. + +The "SNDRV_CARDS" you see being passed in is a "unsigned int ndev" +parameter, indicating how many devices to create and call our methods +with. + +The platform_driver callbacks are called with a platform_device param; +the isa_driver callbacks are being called with a "struct device *dev, +unsigned int id" pair directly -- with the device creation completely +internal to the bus it's much cleaner to not leak isa_dev's by passing +them in at all. The id is the only thing we ever want other then the +struct device * anyways, and it makes for nicer code in the callbacks as +well. + +With this additional .match() callback ISA drivers have all options. If +ALSA would want to keep the old non-load behaviour, it could stick all +of the old .probe in .match, which would only keep them registered after +everything was found to be present and accounted for. If it wanted the +behaviour of always loading as it inadvertently did for a bit after the +changeover to platform devices, it could just not provide a .match() and +do everything in .probe() as before. + +If it, as Takashi Iwai already suggested earlier as a way of following +the model from saner buses more closely, wants to load when a later bind +could conceivably succeed, it could use .match() for the prerequisites +(such as checking the user wants the card enabled and that port/irq/dma +values have been passed in) and .probe() for everything else. This is +the nicest model. + +To the code... + +This exports only two functions; isa_{,un}register_driver(). + +isa_register_driver() register's the struct device_driver, and then +loops over the passed in ndev creating devices and registering them. +This causes the bus match method to be called for them, which is: + +int isa_bus_match(struct device *dev, struct device_driver *driver) +{ + struct isa_driver *isa_driver = to_isa_driver(driver); + + if (dev->platform_data == isa_driver) { + if (!isa_driver->match || + isa_driver->match(dev, to_isa_dev(dev)->id)) + return 1; + dev->platform_data = NULL; + } + return 0; +} + +The first thing this does is check if this device is in fact one of this +driver's devices by seeing if the device's platform_data pointer is set +to this driver. Platform devices compare strings, but we don't need to +do that with everything being internal, so isa_register_driver() abuses +dev->platform_data as a isa_driver pointer which we can then check here. +I believe platform_data is available for this, but if rather not, moving +the isa_driver pointer to the private struct isa_dev is ofcourse fine as +well. + +Then, if the the driver did not provide a .match, it matches. If it did, +the driver match() method is called to determine a match. + +If it did _not_ match, dev->platform_data is reset to indicate this to +isa_register_driver which can then unregister the device again. + +If during all this, there's any error, or no devices matched at all +everything is backed out again and the error, or -ENODEV, is returned. + +isa_unregister_driver() just unregisters the matched devices and the +driver itself. + +module_isa_driver is a helper macro for ISA drivers which do not do +anything special in module init/exit. This eliminates a lot of +boilerplate code. Each module may only use this macro once, and calling +it replaces module_init and module_exit. + +max_num_isa_dev is a macro to determine the maximum possible number of +ISA devices which may be registered in the I/O port address space given +the address extent of the ISA devices. diff --git a/MAINTAINERS b/MAINTAINERS index 1d5b4becab6f..92a190675ae3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -5995,6 +5995,13 @@ F: include/linux/irqdomain.h F: kernel/irq/irqdomain.c F: kernel/irq/msi.c +ISA +M: William Breathitt Gray <vilhelm.gray@gmail.com> +S: Maintained +F: Documentation/isa.txt +F: drivers/base/isa.c +F: include/linux/isa.h + ISAPNP M: Jaroslav Kysela <perex@perex.cz> S: Maintained |