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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-06-27 15:39:22 -0300 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-15 11:03:02 -0300 |
commit | baa293e9544bea71361950d071579f0e4d5713ed (patch) | |
tree | 29e0400c806016783a3fd7a380be40a201956653 /Documentation/isa.txt | |
parent | 4f4cfa6c560c93ba180c30675cf845e1597de44c (diff) | |
download | linux-stable-baa293e9544bea71361950d071579f0e4d5713ed.tar.gz linux-stable-baa293e9544bea71361950d071579f0e4d5713ed.tar.bz2 linux-stable-baa293e9544bea71361950d071579f0e4d5713ed.zip |
docs: driver-api: add a series of orphaned documents
There are lots of documents under Documentation/*.txt and a few other
orphan documents elsehwere that belong to the driver-API book.
Move them to their right place.
Reviewed-by: Cornelia Huck <cohuck@redhat.com> # vfio-related parts
Acked-by: Logan Gunthorpe <logang@deltatee.com> # switchtec
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/isa.txt')
-rw-r--r-- | Documentation/isa.txt | 122 |
1 files changed, 0 insertions, 122 deletions
diff --git a/Documentation/isa.txt b/Documentation/isa.txt deleted file mode 100644 index def4a7b690b5..000000000000 --- a/Documentation/isa.txt +++ /dev/null @@ -1,122 +0,0 @@ -=========== -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. |