lib/cbmem_top: Add a common cbmem_top implementation

This adds a common cbmem_top implementation to all coreboot target.

In romstage a static variable will be used to cache the result of
cbmem_top_romstage.

In ramstage if CONFIG_RAMSTAGE_CBMEM_TOP_ARG is set a global variable
needs to be populated by the stage entry with the value passed via the
calling arguments. if CONFIG_RAMSTAGE_CBMEM_TOP_ARG is not set the
same implementation as will be used as in romstage.

Change-Id: Ie767542ee25483acc9a56785ce20a885e9a63098
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36273
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/include/cbmem.h b/src/include/cbmem.h
index 4005fa205a7a..a22c420ad3b7 100644
--- a/src/include/cbmem.h
+++ b/src/include/cbmem.h
@@ -73,7 +73,18 @@ void cbmem_top_init(void);
  * below 4GiB for 32bit coreboot builds. On 64bit coreboot builds there's no
  * upper limit. This should not be called before memory is initialized.
  */
+/* The assumption is made that the result of cbmem_top_romstage fits in the size
+   of uintptr_t in the ramstage. */
+extern uintptr_t _cbmem_top_ptr;
 void *cbmem_top(void);
+/* With CONFIG_RAMSTAGE_CBMEM_TOP_ARG set, the result of cbmem_top is passed via
+ * calling arguments to the next stage and saved in the global _cbmem_top_ptr
+ * global variable. Only a romstage callback needs to be implemented by the
+ * platform. It is up to the stages after romstage to save the calling argument
+ * in the _cbmem_top_ptr symbol. Without CONFIG_RAMSTAGE_CBMEM_TOP_ARG the same
+ * implementation as used in romstage will be used.
+ */
+void *cbmem_top_chipset(void);
 
 /* Add a cbmem entry of a given size and id. These return NULL on failure. The
  * add function performs a find first and do not check against the original