sunxi: common VBUS detection logic in usbc

[karo-tx-uboot.git] / README

diff --git a/README b/README
index f6d8a318d431fe9ee24521bd3910894eeccdb97d..3c23d164bd84e07aba2d3b6cd5a8d4383772619d 100644 (file)
--- a/README
+++ b/README
@@ -273,6 +273,75 @@ run some of U-Boot's tests.
 See board/sandbox/README.sandbox for more details.
 
 
+Board Initialisation Flow:
+--------------------------
+
+This is the intended start-up flow for boards. This should apply for both
+SPL and U-Boot proper (i.e. they both follow the same rules). At present SPL
+mostly uses a separate code path, but the funtion names and roles of each
+function are the same. Some boards or architectures may not conform to this.
+At least most ARM boards which use CONFIG_SPL_FRAMEWORK conform to this.
+
+Execution starts with start.S with three functions called during init after
+that. The purpose and limitations of each is described below.
+
+lowlevel_init():
+       - purpose: essential init to permit execution to reach board_init_f()
+       - no global_data or BSS
+       - there is no stack (ARMv7 may have one but it will soon be removed)
+       - must not set up SDRAM or use console
+       - must only do the bare minimum to allow execution to continue to
+               board_init_f()
+       - this is almost never needed
+       - return normally from this function
+
+board_init_f():
+       - purpose: set up the machine ready for running board_init_r():
+               i.e. SDRAM and serial UART
+       - global_data is available
+       - stack is in SRAM
+       - BSS is not available, so you cannot use global/static variables,
+               only stack variables and global_data
+
+       Non-SPL-specific notes:
+       - dram_init() is called to set up DRAM. If already done in SPL this
+               can do nothing
+
+       SPL-specific notes:
+       - you can override the entire board_init_f() function with your own
+               version as needed.
+       - preloader_console_init() can be called here in extremis
+       - should set up SDRAM, and anything needed to make the UART work
+       - these is no need to clear BSS, it will be done by crt0.S
+       - must return normally from this function (don't call board_init_r()
+               directly)
+
+Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
+this point the stack and global_data are relocated to below
+CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
+memory.
+
+board_init_r():
+       - purpose: main execution, common code
+       - global_data is available
+       - SDRAM is available
+       - BSS is available, all static/global variables can be used
+       - execution eventually continues to main_loop()
+
+       Non-SPL-specific notes:
+       - U-Boot is relocated to the top of memory and is now running from
+               there.
+
+       SPL-specific notes:
+       - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
+               CONFIG_SPL_STACK_R_ADDR points into SDRAM
+       - preloader_console_init() can be called here - typically this is
+               done by defining CONFIG_SPL_BOARD_INIT and then supplying a
+               spl_board_init() function containing this call
+       - loads U-Boot or (in falcon mode) Linux
+
+
+
 Configuration Options:
 ----------------------
 
@@ -621,6 +690,11 @@ The following options need to be configured:
                exists, unlike the similar options in the Linux kernel. Do not
                set these options unless they apply!
 
+               NOTE: The following can be machine specific errata. These
+               do have ability to provide rudimentary version and machine
+               specific checks, but expect no product checks.
+               CONFIG_ARM_ERRATA_798870
+
 - Tegra SoC options:
                CONFIG_TEGRA_SUPPORT_NON_SECURE
 
@@ -741,7 +815,6 @@ The following options need to be configured:
 
                Enable removing of devices.
 
-
 - Linux Kernel Interface:
                CONFIG_CLOCKS_IN_MHZ
 
@@ -3531,9 +3604,6 @@ FIT uImage format:
                Adds the MTD partitioning infrastructure from the Linux
                kernel. Needed for UBI support.
 
-               CONFIG_MTD_NAND_VERIFY_WRITE
-               verify if the written data is correct reread.
-
 - UBI support
                CONFIG_CMD_UBI
 
@@ -3658,6 +3728,16 @@ FIT uImage format:
                CONFIG_SPL_STACK
                Adress of the start of the stack SPL will use
 
+               CONFIG_SPL_PANIC_ON_RAW_IMAGE
+               When defined, SPL will panic() if the image it has
+               loaded does not have a signature.
+               Defining this is useful when code which loads images
+               in SPL cannot guarantee that absolutely all read errors
+               will be caught.
+               An example is the LPC32XX MLC NAND driver, which will
+               consider that a completely unreadable NAND block is bad,
+               and thus should be skipped silently.
+
                CONFIG_SPL_RELOC_STACK
                Adress of the start of the stack SPL will use after
                relocation.  If unspecified, this is equal to
@@ -4238,9 +4318,9 @@ Configuration Settings:
        to this new framework over time. Defining this will disable the
        arch/foo/lib/board.c file and use common/board_f.c and
        common/board_r.c instead. To use this option your architecture
-       must support it (i.e. must define __HAVE_ARCH_GENERIC_BOARD in
-       its config.mk file). If you find problems enabling this option on
-       your board please report the problem and send patches!
+       must support it (i.e. must select HAVE_GENERIC_BOARD in arch/Kconfig).
+       If you find problems enabling this option on your board please report
+       the problem and send patches!
 
 - CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC (OMAP only)
        This is set by OMAP boards for the max time that reset should