驱动开发学习笔记. 0.05 linux 2.6 platform device register 平台设备注册 2/2 共2篇

Device Enumeration
82 ~~~~~~~~~~~~~~~~~~
83 As a rule, platform specific (and often board-specific) setup code will
84 register platform devices:
85
86 int platform_device_register(struct platform_device *pdev);
87
88 int platform_add_devices(struct platform_device **pdevs, int ndev);
89
90 The general rule is to register only those devices that actually exist,
91 but in some cases extra devices might be registered. For example, a kernel
92 might be configured to work with an external network adapter that might not
93 be populated on all boards, or likewise to work with an integrated controller
94 that some boards might not hook up to any peripherals.
95
96 In some cases, boot firmware will export tables describing the devices
97 that are populated on a given board. Without such tables, often the
98 only way for system setup code to set up the correct devices is to build
99 a kernel for a specific target board. Such board-specific kernels are
100 common with embedded and custom systems development.
101
102 In many cases, the memory and IRQ resources associated with the platform
103 device are not enough to let the device's driver work. Board setup code
104 will often provide additional information using the device's platform_data
105 field to hold additional information.
106
107 Embedded systems frequently need one or more clocks for platform devices,
108 which are normally kept off until they're actively needed (to save power).
109 System setup also associates those clocks with the device, so that that
110 calls to clk_get(&pdev->dev, clock_name) return them as needed.
111
112
113 Legacy Drivers: Device Probing
114 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
115 Some drivers are not fully converted to the driver model, because they take
116 on a non-driver role: the driver registers its platform device, rather than
117 leaving that for system infrastructure. Such drivers can't be hotplugged
118 or coldplugged, since those mechanisms require device creation to be in a
119 different system component than the driver.
120
121 The only "good" reason for this is to handle older system designs which, like
122 original IBM PCs, rely on error-prone "probe-the-hardware" models for hardware
123 configuration. Newer systems have largely abandoned that model, in favor of
124 bus-level support for dynamic configuration (PCI, USB), or device tables
125 provided by the boot firmware (e.g. PNPACPI on x86). There are too many
126 conflicting options about what might be where, and even educated guesses by
127 an operating system will be wrong often enough to make trouble.
128
129 This style of driver is discouraged. If you're updating such a driver,
130 please try to move the device enumeration to a more appropriate location,
131 outside the driver. This will usually be cleanup, since such drivers
132 tend to already have "normal" modes, such as ones using device nodes that
133 were created by PNP or by platform device setup.
134
135 None the less, there are some APIs to support such legacy drivers. Avoid
136 using these calls except with such hotplug-deficient drivers.
137
138 struct platform_device *platform_device_alloc(
139 const char *name, int id);
140
141 You can use platform_device_alloc() to dynamically allocate a device, which
142 you will then initialize with resources and platform_device_register().
143 A better solution is usually:
144
145 struct platform_device *platform_device_register_simple(
146 const char *name, int id,
147 struct resource *res, unsigned int nres);
148
149 You can use platform_device_register_simple() as a one-step call to allocate
150 and register a device.