soc/qualcomm/ipq40xx: Return NULL for cbmem_top if DRAM is not initialized

DRAM initialization on gale requires ipq blobs to be
loaded from cbfs. vboot_locator first checks cbmem_find to see if cbmem is
initialized and contains selected region info, else it falls back to
vboot work buffer.

Since cbmem_find calls into cbmem_top to identify the location of
cbmem area, board/chipset is expected to return NULL until the backing
store is ready, which in this case until DRAM is initialized in
romstage, return NULL for cbmem_top.

BUG=chrome-os-partner:49249
TEST=Able to compile and boot to depthcharge. Doesn't crash in
imd_handle_init_partial_recovery
BRANCH=none

Change-Id: Iaac24252ee4fb9f59d767730bf9dd68baa42a68f
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 4849c15dee2d3782ede4ee4157e432bd4d5602f0
Original-Change-Id: I3722b7ab5a6585a250138c828eb3d7919b0c1178
Original-Signed-off-by: Varadarajan Narayanan <varada@codeaurora.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/335425
Original-Commit-Ready: David Hendricks <dhendrix@chromium.org>
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: https://review.coreboot.org/14660
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/gale/mmu.c

@@ -12,6 +12,7 @@
 
 #include <arch/cache.h>
 #include <symbols.h>
+#include <soc/soc_services.h>
 #include "mmu.h"
 
 #define WIFI_IMEM_0_START	((uintptr_t)_wifi_imem_0 / KiB)
@@ -33,6 +34,8 @@ void setup_dram_mappings(enum dram_state dram)
 		mmu_config_range(DRAM_START, DRAM_SIZE, DCACHE_WRITEBACK);
 		/* Map DMA memory */
 		mmu_config_range(DMA_START, DMA_SIZE, DCACHE_OFF);
+		/* Mark cbmem backing store as ready. */
+		ipq_cbmem_backing_store_ready();
 	} else {
 		mmu_disable_range(DRAM_START, DRAM_SIZE);
 		/* Map DMA memory */

src/soc/qualcomm/ipq40xx/Makefile.inc

@@ -16,6 +16,7 @@
 ifeq ($(CONFIG_SOC_QC_IPQ40XX),y)
 
 bootblock-y += clock.c
+bootblock-y += cbmem.c
 bootblock-y += gpio.c
 bootblock-$(CONFIG_SPI_FLASH) += spi.c
 bootblock-y += timer.c

src/soc/qualcomm/ipq40xx/cbmem.c

@@ -16,7 +16,23 @@
 #include <cbmem.h>
 #include <soc/soc_services.h>
 
+static int cbmem_backing_store_ready;
+
+void ipq_cbmem_backing_store_ready(void)
+{
+	cbmem_backing_store_ready = 1;
+}
+
 void *cbmem_top(void)
 {
+	/*
+	 * In romstage, make sure that cbmem backing store is ready before
+	 * returning pointer to cbmem top. Otherwise, it could lead to issues
+	 * with components that utilize cbmem in romstage (e.g. vboot_locator
+	 * for loading ipq blobs before DRAM is initialized).
+	 */
+	if (ENV_ROMSTAGE && (cbmem_backing_store_ready == 0))
+		return NULL;
+
 	return _memlayout_cbmem_top;
 }

src/soc/qualcomm/ipq40xx/include/soc/soc_services.h

@@ -32,4 +32,7 @@ int tz_init_wrapper(int, int, void *);
 /* Load RPM code into memory and trigger its execution. */
 void start_rpm(void);
 
+/* Mark cbmem backing store as ready. */
+void ipq_cbmem_backing_store_ready(void);
+
 #endif