common: Add attribute to store const data in .data

On EC chips that support CONFIG_CHIP_DATA_IN_INIT_ROM, the code
execution RAM is smaller than flash, leaving some flash unused.

The CONFIG_CHIP_DATA_IN_INIT_ROM moves the .data section into the unused
flash area, where it is copied directly into data RAM at startup.

Add a new attribute __const_data that allows constant data objects to
link into the .data section instead of .rodata.

This saves 1600 bytes of RO and RW flash space on boards that enable
CONFIG_CHIP_DATA_IN_INIT_ROM.

  delbin_npcx796fc
  eldrid_npcx796fc
  halvor
  lindar
  lingcod
  magolor_legacy
  malefor
  metaknight_legacy
  terrador
  todor
  trondo
  voema
  volteer_apmodeentry
  volteer
  waddledoo

BUG=none
BRANCH=none
TEST=make buildall
TEST=boot Volteer and verify USB-PD operation

Signed-off-by: Keith Short <keithshort@chromium.org>
Change-Id: Ibb97a499442bbab8185b1d07f8867a7af1e793f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2651208
Reviewed-by: Abe Levkoy <alevkoy@chromium.org>

3 files changed, 19 insertions, 5 deletions

diff --git a/common/usbc/usb_pe_drp_sm.c b/common/usbc/usb_pe_drp_sm.c
index 43220525f6..72e09e8b68 100644
--- a/common/usbc/usb_pe_drp_sm.c
+++ b/common/usbc/usb_pe_drp_sm.c
@@ -364,7 +364,7 @@ static const struct usb_state pe_states[];
 #endif
 
 /* List of human readable state names for console debugging */
-__maybe_unused static const char * const pe_state_names[] = {
+__maybe_unused static __const_data const char * const pe_state_names[] = {
 	/* Super States */
 #ifdef CONFIG_USB_PD_REV30
 	[PE_PRS_FRS_SHARED] = "SS:PE_PRS_FRS_SHARED",
@@ -6713,8 +6713,7 @@ uint32_t pe_get_flags(int port)
 	return pe[port].flags;
 }
 
-
-static const struct usb_state pe_states[] = {
+static __const_data const struct usb_state pe_states[] = {
 	/* Super States */
 #ifdef CONFIG_USB_PD_REV30
 	[PE_PRS_FRS_SHARED] = {
diff --git a/common/usbc/usb_tc_drp_acc_trysrc_sm.c b/common/usbc/usb_tc_drp_acc_trysrc_sm.c
index 293f5bf1fa..63984d3666 100644
--- a/common/usbc/usb_tc_drp_acc_trysrc_sm.c
+++ b/common/usbc/usb_tc_drp_acc_trysrc_sm.c
@@ -236,7 +236,7 @@ GEN_NOT_SUPPORTED(TC_CT_ATTACHED_SNK);
 
 
 /* List of human readable state names for console debugging */
-__maybe_unused static const char * const tc_state_names[] = {
+__maybe_unused static __const_data const char * const tc_state_names[] = {
 #ifdef USB_PD_DEBUG_LABELS
 	[TC_DISABLED] = "Disabled",
 	[TC_ERROR_RECOVERY] = "ErrorRecovery",
@@ -3656,7 +3656,7 @@ DECLARE_HOOK(HOOK_CHIPSET_SHUTDOWN, pd_chipset_shutdown, HOOK_PRIO_DEFAULT);
  * TC_ATTACHED_SNK    TC_ATTACHED_SRC    TC_DRP_AUTO_TOGGLE    TC_LOW_POWER_MODE
  *
  */
-static const struct usb_state tc_states[] = {
+static __const_data const struct usb_state tc_states[] = {
 	/* Super States */
 	[TC_CC_OPEN] = {
 		.entry	= tc_cc_open_entry,
diff --git a/include/common.h b/include/common.h
index 86c006d9e9..da3af6dc21 100644
--- a/include/common.h
+++ b/include/common.h
@@ -224,6 +224,21 @@
 /* Include top-level configuration file */
 #include "config.h"
 
+/*
+ * When CONFIG_CHIP_DATA_IN_INIT_ROM is enabled the .data section is linked
+ * into an unused are of flash and excluded from the executable portion of
+ * the RO and RW images to save space.
+ *
+ * The __const_data attribute can be used to force constant data objects
+ * into the .data section instead of the .rodata section for additional
+ * savings.
+ */
+#ifdef CONFIG_CHIP_DATA_IN_INIT_ROM
+#define __const_data __attribute__((section(".data#")))
+#else
+#define __const_data
+#endif
+
 /* Canonical list of module IDs */
 #include "module_id.h"