CBMEM: Add config CBMEM_TOP_BACKUP

AGESA and binaryPI boards have no easy way to determine correct
cbmem_top() location early enough when GFXUMA is enabled, so they
will use these functions with EARLY_CBMEM_INIT as well.

At the end of AmdInitPost() the decisions of UMA base and size
have not been written to hardware yet. The decisions are stored
inside AGESA heap object we cannot locate from coreboot proper
until after AmdInitEnv().

Modify code such that weak backup functions are only defined
for LATE_CBMEM_INIT; they are somewhat troublesome to handle.

Change-Id: Ifef4f75b36bc6dee6cd56d1d9164281d9b2a4f2a
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/19306
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

1 files changed, 21 insertions, 23 deletions

diff --git a/src/arch/x86/cbmem.c b/src/arch/x86/cbmem.c
index 578bb8a4ed..e35d43cecb 100644
--- a/src/arch/x86/cbmem.c
+++ b/src/arch/x86/cbmem.c
@@ -18,49 +18,47 @@
 
 #if IS_ENABLED(CONFIG_LATE_CBMEM_INIT)
 
-#if !defined(__PRE_RAM__)
 void __attribute__((weak)) backup_top_of_ram(uint64_t ramtop)
 {
 	/* Do nothing. Chipset may have implementation to save ramtop in NVRAM.
 	 */
 }
 
-static void *ramtop_pointer;
-
-void set_top_of_ram(uint64_t ramtop)
+unsigned long __attribute__((weak)) get_top_of_ram(void)
 {
-	backup_top_of_ram(ramtop);
-	ramtop_pointer = (void *)(uintptr_t)ramtop;
+	return 0;
 }
 
-static inline void *saved_ramtop(void)
-{
-	return ramtop_pointer;
-}
-#else
-static inline void *saved_ramtop(void)
-{
-	return NULL;
-}
-#endif /* !__PRE_RAM__ */
+#endif /* LATE_CBMEM_INIT */
 
-unsigned long __attribute__((weak)) get_top_of_ram(void)
+#if IS_ENABLED(CONFIG_CBMEM_TOP_BACKUP)
+
+static void *ramtop_pointer;
+
+void set_top_of_ram(uint64_t ramtop)
 {
-	return 0;
+	backup_top_of_ram(ramtop);
+	if (ENV_RAMSTAGE)
+		ramtop_pointer = (void *)(uintptr_t)ramtop;
 }
 
 void *cbmem_top(void)
 {
 	/* Top of cbmem is at lowest usable DRAM address below 4GiB. */
-	void *ptr = saved_ramtop();
+	uintptr_t ramtop;
+
+	if (ENV_RAMSTAGE && ramtop_pointer != NULL)
+		return ramtop_pointer;
 
-	if (ptr != NULL)
-		return ptr;
+	ramtop = get_top_of_ram();
 
-	return (void *)get_top_of_ram();
+	if (ENV_RAMSTAGE)
+		ramtop_pointer = (void *)ramtop;
+
+	return (void *)ramtop;
 }
 
-#endif /* LATE_CBMEM_INIT */
+#endif /* CBMEM_TOP_BACKUP */
 
 /* Something went wrong, our high memory area got wiped */
 void cbmem_fail_resume(void)