into system-on-chip platforms. What they usually have in common
is direct addressing from a CPU bus. Rarely, a platform_device will
be connected through a segment of some other kind of bus; but its
-registers will still be directly addressible.
+registers will still be directly addressable.
Platform devices are given a name, used in driver binding, and a
list of resources such as addresses and IRQs.
Device Enumeration
~~~~~~~~~~~~~~~~~~
-As a rule, platform specific (and often board-specific) setup code wil
+As a rule, platform specific (and often board-specific) setup code will
register platform devices:
int platform_device_register(struct platform_device *pdev);
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(
+ const char *name, int 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(
+ const char *name, int id,
+ struct resource *res, unsigned int 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.
* platform_device.id ... the device instance number, or else "-1"
to indicate there's only one.
-These are catenated, so name/id "serial"/0 indicates bus_id "serial.0", and
+These are concatenated, so name/id "serial"/0 indicates bus_id "serial.0", and
"serial/3" indicates bus_id "serial.3"; both would use the platform_driver
named "serial". While "my_rtc"/-1 would be bus_id "my_rtc" (no instance id)
and use the platform_driver called "my_rtc".
usually register later during booting, or by module loading.
- Registering a driver using platform_driver_probe() works just like
- using platform_driver_register(), except that the the driver won't
+ using platform_driver_register(), except that the driver won't
be probed later if another device registers. (Which is OK, since
this interface is only for use with non-hotpluggable devices.)