dm: Add platform data advice and admonishment

We should guide people more strongly towards device tree to avoid the
proliferation of platform data structures. Add documentation to the driver
model README, and also the platform data header file.

Signed-off-by: Simon Glass <sjg@chromium.org>

diff --git a/doc/driver-model/README.txt b/doc/driver-model/README.txt
index f0276b1b46fe6135f549cf37f7fe5e28c4efd4fe..b891e8459d85f2c6dd946939658e7d72e485a84d 100644 (file)
--- a/doc/driver-model/README.txt
+++ b/doc/driver-model/README.txt
@@ -301,6 +301,15 @@ device tree) and probe.
 Platform Data
 -------------
 
+*** Note: platform data is the old way of doing things. It is
+*** basically a C structure which is passed to drivers to tell them about
+*** platform-specific settings like the address of its registers, bus
+*** speed, etc. Device tree is now the preferred way of handling this.
+*** Unless you have a good reason not to use device tree (the main one
+*** being you need serial support in SPL and don't have enough SRAM for
+*** the cut-down device tree and libfdt libraries) you should stay away
+*** from platform data.
+
 Platform data is like Linux platform data, if you are familiar with that.
 It provides the board-specific information to start up a device.
 
@@ -366,8 +375,12 @@ Device Tree
 -----------
 
 While platdata is useful, a more flexible way of providing device data is
-by using device tree. With device tree we replace the above code with the
-following device tree fragment:
+by using device tree. In U-Boot you should use this where possible. Avoid
+sending patches which make use of the U_BOOT_DEVICE() macro unless strictly
+necessary.
+
+With device tree we replace the above code with the following device tree
+fragment:
 
        red-square {
                compatible = "demo-shape";

diff --git a/include/dm/platdata.h b/include/dm/platdata.h
index fbc8a6b3adda18424bd485a0ea39df981143f55e..6f4f00140e5690f404b3169e2dce4e2c0133e735 100644 (file)
--- a/include/dm/platdata.h
+++ b/include/dm/platdata.h
@@ -16,6 +16,10 @@
 /**
  * struct driver_info - Information required to instantiate a device
  *
+ * NOTE: Avoid using this except in extreme circumstances, where device tree
+ * is not feasible (e.g. serial driver in SPL where <8KB of SRAM is
+ * available). U-Boot's driver model uses device tree for configuration.
+ *
  * @name:      Driver name
  * @platdata:  Driver-specific platform data
  */
@@ -24,6 +28,11 @@ struct driver_info {
        const void *platdata;
 };
 
+/**
+ * NOTE: Avoid using these except in extreme circumstances, where device tree
+ * is not feasible (e.g. serial driver in SPL where <8KB of SRAM is
+ * available). U-Boot's driver model uses device tree for configuration.
+ */
 #define U_BOOT_DEVICE(__name)                                          \
        ll_entry_declare(struct driver_info, __name, driver_info)