exists, unlike the similar options in the Linux kernel. Do not
set these options unless they apply!
+- Driver Model
+ Driver model is a new framework for devices in U-Boot
+ introduced in early 2014. U-Boot is being progressively
+ moved over to this. It offers a consistent device structure,
+ supports grouping devices into classes and has built-in
+ handling of platform data and device tree.
+
+ To enable transition to driver model in a relatively
+ painful fashion, each subsystem can be independently
+ switched between the legacy/ad-hoc approach and the new
+ driver model using the options below. Also, many uclass
+ interfaces include compatibility features which may be
+ removed once the conversion of that subsystem is complete.
+ As a result, the API provided by the subsystem may in fact
+ not change with driver model.
+
+ See doc/driver-model/README.txt for more information.
+
+ CONFIG_DM
+
+ Enable driver model. This brings in the core support,
+ including scanning of platform data on start-up. If
+ CONFIG_OF_CONTROL is enabled, the device tree will be
+ scanned also when available.
+
+ CONFIG_CMD_DM
+
+ Enable driver model test commands. These allow you to print
+ out the driver model tree and the uclasses.
+
+ CONFIG_DM_DEMO
+
+ Enable some demo devices and the 'demo' command. These are
+ really only useful for playing around while trying to
+ understand driver model in sandbox.
+
+ CONFIG_SPL_DM
+
+ Enable driver model in SPL. You will need to provide a
+ suitable malloc() implementation. If you are not using the
+ full malloc() enabled by CONFIG_SYS_SPL_MALLOC_START,
+ consider using CONFIG_SYS_MALLOC_SIMPLE. In that case you
+ must provide CONFIG_SYS_MALLOC_F_LEN to set the size.
+ In most cases driver model will only allocate a few uclasses
+ and devices in SPL, so 1KB should be enable. See
+ CONFIG_SYS_MALLOC_F_LEN for more details on how to enable
+ it.
+
+ CONFIG_DM_SERIAL
+
+ Enable driver model for serial. This replaces
+ drivers/serial/serial.c with the serial uclass, which
+ implements serial_putc() etc. The uclass interface is
+ defined in include/serial.h.
+
+ CONFIG_DM_GPIO
+
+ Enable driver model for GPIO access. The standard GPIO
+ interface (gpio_get_value(), etc.) is then implemented by
+ the GPIO uclass. Drivers provide methods to query the
+ particular GPIOs that they provide. The uclass interface
+ is defined in include/asm-generic/gpio.h.
+
+ CONFIG_DM_SPI
+
+ Enable driver model for SPI. The SPI slave interface
+ (spi_setup_slave(), spi_xfer(), etc.) is then implemented by
+ the SPI uclass. Drivers provide methods to access the SPI
+ buses that they control. The uclass interface is defined in
+ include/spi.h. The existing spi_slave structure is attached
+ as 'parent data' to every slave on each bus. Slaves
+ typically use driver-private data instead of extending the
+ spi_slave structure.
+
+ CONFIG_DM_SPI_FLASH
+
+ Enable driver model for SPI flash. This SPI flash interface
+ (spi_flash_probe(), spi_flash_write(), etc.) is then
+ implemented by the SPI flash uclass. There is one standard
+ SPI flash driver which knows how to probe most chips
+ supported by U-Boot. The uclass interface is defined in
+ include/spi_flash.h, but is currently fully compatible
+ with the old interface to avoid confusion and duplication
+ during the transition parent. SPI and SPI flash must be
+ enabled together (it is not possible to use driver model
+ for one and not the other).
+
+ CONFIG_DM_CROS_EC
+
+ Enable driver model for the Chrome OS EC interface. This
+ allows the cros_ec SPI driver to operate with CONFIG_DM_SPI
+ but otherwise makes few changes. Since cros_ec also supports
+ I2C and LPC (which don't support driver model yet), a full
+ conversion is not yet possible.
+
+
+ ** Code size options: The following options are enabled by
+ default except in SPL. Enable them explicitly to get these
+ features in SPL.
+
+ CONFIG_DM_WARN
+
+ Enable the dm_warn() function. This can use up quite a bit
+ of space for its strings.
+
+ CONFIG_DM_STDIO
+
+ Enable registering a serial device with the stdio library.
+
+ CONFIG_DM_DEVICE_REMOVE
+
+ Enable removing of devices.
+
+
- Linux Kernel Interface:
CONFIG_CLOCKS_IN_MHZ
Pre-relocation malloc() is only supported on ARM and sandbox
at present but is fairly easy to enable for other archs.
+- CONFIG_SYS_MALLOC_SIMPLE
+ Provides a simple and small malloc() and calloc() for those
+ boards which do not use the full malloc in SPL (which is
+ enabled with CONFIG_SYS_SPL_MALLOC_START).
+
- CONFIG_SYS_BOOTM_LEN:
Normally compressed uImages are limited to an
uncompressed size of 8 MBytes. If this is not enough,
pointer is saved but not made available through the driver model API).
-Things to punt for later
-------------------------
+SPL Support
+-----------
+
+Driver model can operate in SPL. Its efficient implementation and small code
+size provide for a small overhead which is acceptable for all but the most
+constrained systems.
+
+To enable driver model in SPL, define CONFIG_SPL_DM. You might want to
+consider the following option also. See the main README for more details.
+
+ - CONFIG_SYS_MALLOC_SIMPLE
+ - CONFIG_DM_WARN
+ - CONFIG_DM_DEVICE_REMOVE
+ - CONFIG_DM_STDIO
-- SPL support - this will have to be present before many drivers can be
-converted, but it seems like we can add it once we are happy with the
-core implementation.
-That is not to say that no thinking has gone into this - in fact there
-is quite a lot there. However, getting these right is non-trivial and
-there is a high cost associated with going down the wrong path.
+Enabling Driver Model
+---------------------
-For SPL, it may be possible to fit in a simplified driver model with only
-bind and probe methods, to reduce size.
+Driver model is being brought into U-Boot gradually. As each subsystems gets
+support, a uclass is created and a CONFIG to enable use of driver model for
+that subsystem.
+
+For example CONFIG_DM_SERIAL enables driver model for serial. With that
+defined, the old serial support is not enabled, and your serial driver must
+conform to driver model. With that undefined, the old serial support is
+enabled and driver model is not available for serial. This means that when
+you convert a driver, you must either convert all its boards, or provide for
+the driver to be compiled both with and without driver model (generally this
+is not very hard).
+
+See the main README for full details of the available driver model CONFIG
+options.
+
+
+Things to punt for later
+------------------------
Uclasses are statically numbered at compile time. It would be possible to
change this to dynamic numbering, but then we would require some sort of
projects / u-boot / commitdiff