Commit:     adfdebceaca988515ecdb557d600fd5ab9da913a
Parent:     85f6038f2170e3335dda09c3dfb0f83110e87019
Author:     David Brownell <[EMAIL PROTECTED]>
AuthorDate: Thu May 10 22:36:14 2007 -0700
Committer:  Greg Kroah-Hartman <[EMAIL PROTECTED]>
CommitDate: Fri Jun 8 12:41:07 2007 -0700

    update Documentation/driver-model/platform.txt
    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 <[EMAIL PROTECTED]>
    Cc: Andres Salomon <[EMAIL PROTECTED]>
    Cc: Dmitry Torokhov <[EMAIL PROTECTED]>
    Cc: Russell King <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Greg Kroah-Hartman <[EMAIL PROTECTED]>
 Documentation/driver-model/platform.txt |   40 +++++++++++++++++++++++++++++++
 1 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/Documentation/driver-model/platform.txt 
index 19c4a6e..2a97320 100644
--- a/Documentation/driver-model/platform.txt
+++ b/Documentation/driver-model/platform.txt
@@ -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 is the canonical name for the devices.
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