x86: provide consistent cbmem_top() for CONFIG_LATE_CBMEM_INIT

For x86 systems employing CONFIG_LATE_CBMEM_INIT, set_top_of_ram() is
called in ramstage to note the upper address of the 32-bit address
space. This in turn is consumed by cbmem. However, in this scenario
cbmem_top() cannot always be relied upon because get_top_of_ram()
doesn't return the same value provided to set_top_of_ram().
To fix the inconsistency in ramstage save the value passed in
to set_top_of_ram() and defer to it as the return value for
cbmem_top().

Change-Id: Ida796fb836c59b9776019e7f8b3f2cd71156f0e5
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10313
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/include/cbmem.h b/src/include/cbmem.h
index 20cc174d05..0a7ca89cd4 100644
--- a/src/include/cbmem.h
+++ b/src/include/cbmem.h
@@ -221,6 +221,9 @@ void cbmem_list(void);
  * early features like COLLECT_TIMESTAMPS and CBMEM_CONSOLE.
  */
 #if IS_ENABLED(CONFIG_ARCH_X86) && IS_ENABLED(CONFIG_LATE_CBMEM_INIT)
+/* Note that many of the current providers of get_top_of_ram() conditionally
+ * return 0 when the sleep type is non S3. i.e. cold and warm boots would
+ * return 0 from get_top_of_ram(). */
 unsigned long get_top_of_ram(void);
 void set_top_of_ram(uint64_t ramtop);
 void backup_top_of_ram(uint64_t ramtop);