system: Add support to reclaim space from loader.

Certain ECs which cannot load both the RO and RW images into memory
simultaneously have a little firmware (LFW) loader that is loaded into
the beginning of the program memory.  This loader is responsible for
loading the RO/RW images, however once we begin executing code from
main(), the loader has already completed it's purpose.  We can reuse
this space by allocating portions of the .bss section here.  This
currently saves us 3k for mec1322.  This section is .bss.slow.

To use this feature simply define the following config option in
board.h.

  #define CONFIG_REPLACE_LOADER_WITH_BSS_SLOW

In some cases, such as the mec1322, this region of RAM is optimized for
code and not data.  Therefore, ideally infrequently used data should go
into this region.

BUG=chrome-os-partner:46056
BUG=chrome-os-partner:46063
BRANCH=None
TEST=Flash GLaDOS; sysjump rw; Verify that we are in rw; sysjump ro;
Verify we are back in ro.
TEST=Build GLaDOS, check output memory map for LDR_REGION and .bss.slow
section.
TEST=make -j buildall tests

Change-Id: I5b95cacc211278cf780a857b5a2ecfc1a0a28c45
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/305254
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-by: Shawn N <shawnn@chromium.org>

4 files changed, 54 insertions, 0 deletions

diff --git a/common/main.c b/common/main.c
index 016d4f6279..bafb18c94a 100644
--- a/common/main.c
+++ b/common/main.c
@@ -25,6 +25,7 @@
 #include "task.h"
 #include "timer.h"
 #include "uart.h"
+#include "util.h"
 #include "watchdog.h"
 
 /* Console output macros */
@@ -34,6 +35,15 @@
 
 test_mockable __keep int main(void)
 {
+#ifdef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+	/*
+	 * Now that we have started execution, we no longer need the loader.
+	 * Instead, variables placed in the .bss.slow section will use this
+	 * space.  Therefore, clear out this region now.
+	 */
+	memset((void *)(CONFIG_PROGRAM_MEMORY_BASE + CONFIG_LOADER_MEM_OFF), 0,
+	       CONFIG_LOADER_SIZE);
+#endif /* defined(CONFIG_REPLACE_LOADER_WITH_BSS_SLOW) */
 	/*
 	 * Pre-initialization (pre-verified boot) stage.  Initialization at
 	 * this level should do as little as possible, because verified boot
diff --git a/common/system.c b/common/system.c
index 4e06d7abc2..224ae7d78e 100644
--- a/common/system.c
+++ b/common/system.c
@@ -26,6 +26,7 @@
 #include "usb_pd.h"
 #include "util.h"
 #include "version.h"
+#include "watchdog.h"
 
 /* Console output macros */
 #define CPUTS(outstr) cputs(CC_SYSTEM, outstr)
@@ -478,6 +479,12 @@ int system_run_image_copy(enum system_image_copy_t copy)
 {
 	uintptr_t base;
 	uintptr_t init_addr;
+#ifdef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+	uint8_t *buf;
+	uint32_t offset;
+	uint32_t bytes_to_load;
+	int rv;
+#endif /* defined(CONFIG_REPLACE_LOADER_WITH_BSS_SLOW) */
 
 	/* If system is already running the requested image, done */
 	if (system_get_image_copy() == copy)
@@ -506,6 +513,22 @@ int system_run_image_copy(enum system_image_copy_t copy)
 		return EC_ERROR_INVAL;
 
 #ifdef CONFIG_EXTERNAL_STORAGE
+#ifdef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+	/*
+	 * We've used the region in which the loader resided as data space for
+	 * the .bss.slow section.  Therefore, we need to reload the loader from
+	 * the external storage back into program memory so that we can load a
+	 * different image.
+	 */
+	buf = (uint8_t *)(CONFIG_PROGRAM_MEMORY_BASE + CONFIG_LOADER_MEM_OFF);
+	bytes_to_load = CONFIG_LOADER_SIZE;
+	offset = CONFIG_EC_PROTECTED_STORAGE_OFF + CONFIG_LOADER_STORAGE_OFF;
+
+	rv = flash_read(offset, bytes_to_load, buf);
+	if (rv)
+		return rv;
+#endif /* defined(CONFIG_REPLACE_LOADER_WITH_BSS_SLOW) */
+
 	/* Jump to loader */
 	init_addr = system_get_lfw_address();
 
diff --git a/core/cortex-m/ec.lds.S b/core/cortex-m/ec.lds.S
index 3e026331fe..f778ca8f88 100644
--- a/core/cortex-m/ec.lds.S
+++ b/core/cortex-m/ec.lds.S
@@ -36,6 +36,11 @@ MEMORY
 
     IRAM (rw)  : ORIGIN = CONFIG_RAM_BASE, LENGTH = CONFIG_RAM_SIZE
 #ifdef CONFIG_EXTERNAL_STORAGE
+#ifdef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+   LDR_REGION(rw) : \
+        ORIGIN = CONFIG_PROGRAM_MEMORY_BASE + CONFIG_LOADER_MEM_OFF, \
+        LENGTH = CONFIG_LOADER_SIZE
+#endif /* defined(CONFIG_REPLACE_LOADER_WITH_BSS_SLOW) */
    CDRAM (rx) : \
         ORIGIN = CONFIG_PROGRAM_MEMORY_BASE + FW_MEM_OFF(SECTION), \
         LENGTH = FW_SIZE(SECTION)
@@ -221,6 +226,16 @@ SECTIONS
         . = ALIGN(4);
         __bss_end = .;
     } > IRAM
+
+    .bss.slow : {
+	/* Region of RAM reclaimed from the little firmware(LFW). */
+	*(.bss.slow)
+#ifdef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+    } > LDR_REGION
+#else
+    } > IRAM
+#endif /* defined(CONFIG_REPLACE_LOADER_WITH_BSS_SLOW) */
+
 #ifdef CONFIG_EXTERNAL_STORAGE
     .data : AT(LOADADDR(.rodata) + SIZEOF(.rodata)) {
 #else
diff --git a/include/config.h b/include/config.h
index 76bae7e9a2..1e017fe028 100644
--- a/include/config.h
+++ b/include/config.h
@@ -793,6 +793,12 @@
 #undef CONFIG_FW_PSTATE_SIZE
 
 /*
+ * Reuse the space that was occupied in RAM by the little firmware (LFW) loader
+ * with the section ".bss.slow" instead.
+ */
+#undef CONFIG_REPLACE_LOADER_WITH_BSS_SLOW
+
+/*
  * Read-only / read-write image configuration.
  * Images may reside on storage (ex. external or internal SPI) at a different
  * offset than when copied to program memory. Hence, two sets of offsets,