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Merge master.kernel.org:/pub/scm/linux/kernel/git/gregkh/driver-2.6
* master.kernel.org:/pub/scm/linux/kernel/git/gregkh/driver-2.6: (36 commits) Driver core: show drivers in /sys/module/ Documentation/driver-model/platform.txt update/rewrite Driver core: platform_driver_probe(), can save codespace driver core: Use klist_remove() in device_move() driver core: Introduce device_move(): move a device to a new parent. Driver core: make drivers/base/core.c:setup_parent() static driver core: Introduce device_find_child(). sysfs: sysfs_write_file() writes zero terminated data cpu topology: consider sysfs_create_group return value Driver core: Call platform_notify_remove later ACPI: Change ACPI to use dev_archdata instead of firmware_data Driver core: add dev_archdata to struct device Driver core: convert sound core to use struct device Driver core: change mem class_devices to be real devices Driver core: convert fb code to use struct device Driver core: convert firmware code to use struct device Driver core: convert mmc code to use struct device Driver core: convert ppdev code to use struct device Driver core: convert PPP code to use struct device Driver core: convert cpuid code to use struct device ...
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| Platform Devices and Drivers | ||
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | ||
| See <linux/platform_device.h> for the driver model interface to the | ||
| platform bus: platform_device, and platform_driver. This pseudo-bus | ||
| is used to connect devices on busses with minimal infrastructure, | ||
| like those used to integrate peripherals on many system-on-chip | ||
| processors, or some "legacy" PC interconnects; as opposed to large | ||
| formally specified ones like PCI or USB. | ||
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| Platform devices | ||
| ~~~~~~~~~~~~~~~~ | ||
| Platform devices are devices that typically appear as autonomous | ||
| entities in the system. This includes legacy port-based devices and | ||
| host bridges to peripheral buses. | ||
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| Platform drivers | ||
| ~~~~~~~~~~~~~~~~ | ||
| Drivers for platform devices are typically very simple and | ||
| unstructured. Either the device was present at a particular I/O port | ||
| and the driver was loaded, or it was not. There was no possibility | ||
| of hotplugging or alternative discovery besides probing at a specific | ||
| I/O address and expecting a specific response. | ||
| host bridges to peripheral buses, and most controllers integrated | ||
| 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. | ||
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| Platform devices are given a name, used in driver binding, and a | ||
| list of resources such as addresses and IRQs. | ||
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| Other Architectures, Modern Firmware, and new Platforms | ||
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | ||
| These devices are not always at the legacy I/O ports. This is true on | ||
| other architectures and on some modern architectures. In most cases, | ||
| the drivers are modified to discover the devices at other well-known | ||
| ports for the given platform. However, the firmware in these systems | ||
| does usually know where exactly these devices reside, and in some | ||
| cases, it's the only way of discovering them. | ||
| struct platform_device { | ||
| const char *name; | ||
| u32 id; | ||
| struct device dev; | ||
| u32 num_resources; | ||
| struct resource *resource; | ||
| }; | ||
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| The Platform Bus | ||
| ~~~~~~~~~~~~~~~~ | ||
| A platform bus has been created to deal with these issues. First and | ||
| foremost, it groups all the legacy devices under a common bus, and | ||
| gives them a common parent if they don't already have one. | ||
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| But, besides the organizational benefits, the platform bus can also | ||
| accommodate firmware-based enumeration. | ||
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| Device Discovery | ||
| Platform drivers | ||
| ~~~~~~~~~~~~~~~~ | ||
| The platform bus has no concept of probing for devices. Devices | ||
| discovery is left up to either the legacy drivers or the | ||
| firmware. These entities are expected to notify the platform of | ||
| devices that it discovers via the bus's add() callback: | ||
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| platform_bus.add(parent,bus_id). | ||
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| Bus IDs | ||
| ~~~~~~~ | ||
| Bus IDs are the canonical names for the devices. There is no globally | ||
| standard addressing mechanism for legacy devices. In the IA-32 world, | ||
| we have Pnp IDs to use, as well as the legacy I/O ports. However, | ||
| neither tell what the device really is or have any meaning on other | ||
| platforms. | ||
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| Since both PnP IDs and the legacy I/O ports (and other standard I/O | ||
| ports for specific devices) have a 1:1 mapping, we map the | ||
| platform-specific name or identifier to a generic name (at least | ||
| within the scope of the kernel). | ||
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| For example, a serial driver might find a device at I/O 0x3f8. The | ||
| ACPI firmware might also discover a device with PnP ID (_HID) | ||
| PNP0501. Both correspond to the same device and should be mapped to the | ||
| canonical name 'serial'. | ||
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| The bus_id field should be a concatenation of the canonical name and | ||
| the instance of that type of device. For example, the device at I/O | ||
| port 0x3f8 should have a bus_id of "serial0". This places the | ||
| responsibility of enumerating devices of a particular type up to the | ||
| discovery mechanism. But, they are the entity that should know best | ||
| (as opposed to the platform bus driver). | ||
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| Drivers | ||
| ~~~~~~~ | ||
| Drivers for platform devices should have a name that is the same as | ||
| the canonical name of the devices they support. This allows the | ||
| platform bus driver to do simple matching with the basic data | ||
| structures to determine if a driver supports a certain device. | ||
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| For example, a legacy serial driver should have a name of 'serial' and | ||
| register itself with the platform bus. | ||
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| Driver Binding | ||
| ~~~~~~~~~~~~~~ | ||
| Legacy drivers assume they are bound to the device once they start up | ||
| and probe an I/O port. Divorcing them from this will be a difficult | ||
| process. However, that shouldn't prevent us from implementing | ||
| firmware-based enumeration. | ||
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| The firmware should notify the platform bus about devices before the | ||
| legacy drivers have had a chance to load. Once the drivers are loaded, | ||
| they driver model core will attempt to bind the driver to any | ||
| previously-discovered devices. Once that has happened, it will be free | ||
| to discover any other devices it pleases. | ||
| Platform drivers follow the standard driver model convention, where | ||
| discovery/enumeration is handled outside the drivers, and drivers | ||
| provide probe() and remove() methods. They support power management | ||
| and shutdown notifications using the standard conventions. | ||
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| struct platform_driver { | ||
| int (*probe)(struct platform_device *); | ||
| int (*remove)(struct platform_device *); | ||
| void (*shutdown)(struct platform_device *); | ||
| int (*suspend)(struct platform_device *, pm_message_t state); | ||
| int (*suspend_late)(struct platform_device *, pm_message_t state); | ||
| int (*resume_early)(struct platform_device *); | ||
| int (*resume)(struct platform_device *); | ||
| struct device_driver driver; | ||
| }; | ||
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| Note that probe() should general verify that the specified device hardware | ||
| actually exists; sometimes platform setup code can't be sure. The probing | ||
| can use device resources, including clocks, and device platform_data. | ||
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| Platform drivers register themselves the normal way: | ||
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| int platform_driver_register(struct platform_driver *drv); | ||
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| Or, in common situations where the device is known not to be hot-pluggable, | ||
| the probe() routine can live in an init section to reduce the driver's | ||
| runtime memory footprint: | ||
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| int platform_driver_probe(struct platform_driver *drv, | ||
| int (*probe)(struct platform_device *)) | ||
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| Device Enumeration | ||
| ~~~~~~~~~~~~~~~~~~ | ||
| As a rule, platform specific (and often board-specific) setup code wil | ||
| register platform devices: | ||
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| int platform_device_register(struct platform_device *pdev); | ||
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| int platform_add_devices(struct platform_device **pdevs, int ndev); | ||
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| The general rule is to register only those devices that actually exist, | ||
| but in some cases extra devices might be registered. For example, a kernel | ||
| might be configured to work with an external network adapter that might not | ||
| be populated on all boards, or likewise to work with an integrated controller | ||
| that some boards might not hook up to any peripherals. | ||
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| In some cases, boot firmware will export tables describing the devices | ||
| that are populated on a given board. Without such tables, often the | ||
| only way for system setup code to set up the correct devices is to build | ||
| a kernel for a specific target board. Such board-specific kernels are | ||
| common with embedded and custom systems development. | ||
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| In many cases, the memory and IRQ resources associated with the platform | ||
| device are not enough to let the device's driver work. Board setup code | ||
| will often provide additional information using the device's platform_data | ||
| field to hold additional information. | ||
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| Embedded systems frequently need one or more clocks for platform devices, | ||
| which are normally kept off until they're actively needed (to save power). | ||
| System setup also associates those clocks with the device, so that that | ||
| calls to clk_get(&pdev->dev, clock_name) return them as needed. | ||
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| Device Naming and Driver Binding | ||
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | ||
| The platform_device.dev.bus_id is the canonical name for the devices. | ||
| It's built from two components: | ||
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| * platform_device.name ... which is also used to for driver matching. | ||
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| * platform_device.id ... the device instance number, or else "-1" | ||
| to indicate there's only one. | ||
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| These are catenated, 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". | ||
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| Driver binding is performed automatically by the driver core, invoking | ||
| driver probe() after finding a match between device and driver. If the | ||
| probe() succeeds, the driver and device are bound as usual. There are | ||
| three different ways to find such a match: | ||
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| - Whenever a device is registered, the drivers for that bus are | ||
| checked for matches. Platform devices should be registered very | ||
| early during system boot. | ||
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| - When a driver is registered using platform_driver_register(), all | ||
| unbound devices on that bus are checked for matches. Drivers | ||
| usually register later during booting, or by module loading. | ||
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| - Registering a driver using platform_driver_probe() works just like | ||
| using platform_driver_register(), except that the 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.) | ||
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