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update Documentation/driver-model/platform.txt

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Make note of the legacy "probe-the-hardware" drivers, and some APIs that
are mostly unused except by such drivers.  We probably can't escape having
legacy drivers for a while (e.g.  old ISA drivers), but we can at least
discourage this style code for new drivers, and unless it's unavoidable.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Andres Salomon <dilinger@debian.org>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
David Brownell 2007-05-10 22:36:14 -07:00 committed by Greg Kroah-Hartman
parent 85f6038f21
commit adfdebceac
1 changed files with 40 additions and 0 deletions
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Documentation/driver-model/platform.txt
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@ -96,6 +96,46 @@ System setup also associates those clocks with the device, so that that
calls to clk_get(&pdev->dev, clock_name) return them as needed.
Legacy Drivers: Device Probing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some drivers are not fully converted to the driver model, because they take
on a non-driver role: the driver registers its platform device, rather than
leaving that for system infrastructure. Such drivers can't be hotplugged
or coldplugged, since those mechanisms require device creation to be in a
different system component than the driver.
The only "good" reason for this is to handle older system designs which, like
original IBM PCs, rely on error-prone "probe-the-hardware" models for hardware
configuration. Newer systems have largely abandoned that model, in favor of
bus-level support for dynamic configuration (PCI, USB), or device tables
provided by the boot firmware (e.g. PNPACPI on x86). There are too many
conflicting options about what might be where, and even educated guesses by
an operating system will be wrong often enough to make trouble.
This style of driver is discouraged. If you're updating such a driver,
please try to move the device enumeration to a more appropriate location,
outside the driver. This will usually be cleanup, since such drivers
tend to already have "normal" modes, such as ones using device nodes that
were created by PNP or by platform device setup.
None the less, there are some APIs to support such legacy drivers. Avoid
using these calls except with such hotplug-deficient drivers.
struct platform_device *platform_device_alloc(
char *name, unsigned id);
You can use platform_device_alloc() to dynamically allocate a device, which
you will then initialize with resources and platform_device_register().
A better solution is usually:
struct platform_device *platform_device_register_simple(
char *name, unsigned id,
struct resource *res, unsigned nres);
You can use platform_device_register_simple() as a one-step call to allocate
and register a device.
Device Naming and Driver Binding
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The platform_device.dev.bus_id is the canonical name for the devices.