dm: core: Add an option to support SPL in read-only memory

Some systems (e.g. x86 APL) run SPL from read-only memory. The device
instances created by dtoc are therefore not writeable. To make things work
we would need to copy the devices to read/write memory.

To avoid this, add an option to use a separate runtime struct for devices,
just as is done for drivers. This can be used to hold information that
changes at runtime, avoiding the need for a copy.

Also add a Kconfig option for read-only SPL, which selects this feature.

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

common/spl/Kconfig

@@ -276,6 +276,19 @@ config SPL_SEPARATE_BSS
 	  location is used. Normally we put the device tree at the end of BSS
 	  but with this option enabled, it goes at _image_binary_end.
 
+config SPL_READ_ONLY
+	bool
+	depends on SPL_OF_PLATDATA
+	# Bind cannot be supported because the udevice structs are in read-only
+	# memory so we cannot update the linked lists.
+	select SPL_OF_PLATDATA_NO_BIND
+	select SPL_OF_PLATDATA_RT
+	help
+	  Some platforms (e.g. x86 Apollo Lake) load SPL into a read-only
+	  section of memory. This means that of-platdata must make a copy (in
+	  writeable memory) of anything it wants to modify, such as
+	  device-private data.
+
 config SPL_BANNER_PRINT
 	bool "Enable output of the SPL banner 'U-Boot SPL ...'"
 	default y
@@ -1440,6 +1453,17 @@ config TPL_STACK
 	  The address of the initial stack-pointer for the TPL stage.
 	  Usually this will be the (aligned) top-of-stack.
 
+config TPL_READ_ONLY
+	bool
+	depends on TPL_OF_PLATDATA
+	select TPL_OF_PLATDATA_NO_BIND
+	select TPL_OF_PLATDATA_RT
+	help
+	  Some platforms (e.g. x86 Apollo Lake) load SPL into a read-only
+	  section of memory. This means that of-platdata must make a copy (in
+	  writeable memory) of anything it wants to modify, such as
+	  device-private data.
+
 config TPL_BOOTROM_SUPPORT
         bool "Support returning to the BOOTROM (from TPL)"
 	help

dts/Kconfig

@@ -380,6 +380,17 @@ config SPL_OF_PLATDATA_NO_BIND
 	  some code space in U-Boot. This can be disabled if binding is needed,
 	  at the code of some code size increase.
 
+config SPL_OF_PLATDATA_RT
+	bool "Use a separate struct for device runtime data"
+	depends on SPL_OF_PLATDATA_INST
+	default y
+	help
+	  For systems running SPL from read-only memory it is convenient to
+	  separate out the runtime information, so that the devices don't need
+	  to be copied before being used. This moves the read-write parts of
+	  struct udevice (at present just the flags) into a separate struct,
+	  which is allocated at runtime.
+
 endif
 
 config TPL_OF_PLATDATA
@@ -429,6 +440,17 @@ config TPL_OF_PLATDATA_NO_BIND
 	  some code space in U-Boot. This can be disabled if binding is needed,
 	  at the code of some code size increase.
 
+config TPL_OF_PLATDATA_RT
+	bool "Use a separate struct for device runtime data"
+	depends on TPL_OF_PLATDATA_INST
+	default y
+	help
+	  For systems running TPL from read-only memory it is convenient to
+	  separate out the runtime information, so that the devices don't need
+	  to be copied before being used. This moves the read-write parts of
+	  struct udevice (at present just the flags) into a separate struct,
+	  which is allocated at runtime.
+
 endif
 
 endmenu