npcx: add support for rom resident sections

EC images are copied in full from flash to RAM. When the code RAM size
is smaller than 1/2 the flash size, the EC image size is limited to the
code RAM size, leaving unused flash space.

Create a new linker section .init_rom used to store data objects that
are single use in the previously unused flash area. Data objects can be
used at runtime by copying into RAM using the flash_read() function.

This change is tied to the NPCX flash layout, with asserts to ensure
builds fail if the CONFIG_CHIP_INIT_ROM_REGION is not supported by
the chip.

CLs that enable CONFIG_CHIP_INIT_ROM_REGION should not be merged until
the predecessor CL:2325764 is available in CPFE images.

BUG=b:160330682
BRANCH=none
TEST=make buildall
TEST=With debug code, use the _init_rom macro and validate the data can
be read using flash_read().
TEST=Using hex editor, verify .init_rom section located at 192K boundary
and unused bytes are filled with 0xFF.
TEST=compare_build.sh passes when run against waddledoo (npcx, cortex-m)

Signed-off-by: Keith Short <keithshort@chromium.org>
Change-Id: Ia0785798fd1938ad6a1c254a070b219027ee82a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2311268
Reviewed-by: caveh jalali <caveh@chromium.org>
Commit-Queue: caveh jalali <caveh@chromium.org>

2 files changed, 71 insertions, 0 deletions

diff --git a/include/common.h b/include/common.h
index c9a61545e6..92731182dc 100644
--- a/include/common.h
+++ b/include/common.h
@@ -111,6 +111,19 @@
 #define __bss_slow __attribute__((section(".bss.slow")))
 #endif
 
+/*
+ * Place a read-only object into a ROM resident section. If supported by the
+ * EC chip, the object is part of the flash image but not copied into RAM
+ * automatically. Users may only access the data using the include/init_rom.h
+ * module.
+ *
+ * Requires CONFIG_CHIP_INIT_ROM_REGION is defined, otherwise the object is
+ * linked into the .rodata section.
+ */
+#ifndef __init_rom
+#define __init_rom __attribute__((section(".init.rom")))
+#endif
+
 /* gcc does not support __has_feature */
 #ifndef __has_feature
 #define __has_feature(x) 0
diff --git a/include/config.h b/include/config.h
index aa8ead6ba1..f80eac0513 100644
--- a/include/config.h
+++ b/include/config.h
@@ -1091,6 +1091,18 @@
  */
 #undef CONFIG_CHIP_UNCACHED_REGION
 
+/*
+ * When defined, adds a new linker section to store objects that remain resident
+ * in ROM/flash. This is useful on ECs that execute all code from RAM and
+ * in which the RAM size is smaller than the flash size.
+ *
+ * Code can force objects into the .init_rom resident section using the
+ * __init_rom macro. Objects should accessed using the include/init_rom.h
+ * module.
+ */
+#undef CONFIG_CHIP_INIT_ROM_REGION
+
+
 /*****************************************************************************/
 /* Chipset config */
 
@@ -1817,6 +1829,24 @@
 #undef CONFIG_RW_SIZE
 
 /*
+ * Offset relative to CONFIG_EC_PROTECTED_STORAGE_OFF
+ * These define a region of flash used to store ROM resident data objects
+ * for RO images.  This is only possible when the program memory is smaller
+ * than CONFIG_EC_PROTECTED_STORAGE_SIZE.
+ */
+#undef CONFIG_RO_ROM_RESIDENT_MEM_OFF
+#undef CONFIG_RO_ROM_RESIDENT_SIZE
+
+/*
+ * Offset relative to CONFIG_EC_WRITABLE_STORAGE_OFF
+ * These define a region of flash used to store ROM resident data objects
+ * for RW images.  This is only possible when the program memory is smaller
+ * than CONFIG_EC_WRITABLE_STORAGE_SIZE.
+ */
+#undef CONFIG_RW_ROM_RESIDENT_MEM_OFF
+#undef CONFIG_RW_ROM_RESIDENT_SIZE
+
+/*
  * NPCX-specific bootheader geometry.
  * TODO(crosbug.com/p/23796): Factor these CONFIGs out.
  */
@@ -5347,6 +5377,34 @@
 #define CONFIG_USB_PD_TBT_GEN3_CAPABLE
 #endif /* CONFIG_USB_PD_TBT_COMPAT_MODE */
 
+/*
+ * CONFIG_CHIP_INIT_ROM_REGION requires that the chip has defined a
+ * ROM resident region to store the .init_rom section.
+ *
+ * These sections must also not be zero bytes, which will happen if
+ * the program size is the same as the flash size.
+ */
+#ifdef CONFIG_CHIP_INIT_ROM_REGION
+
+#ifndef CONFIG_RO_ROM_RESIDENT_SIZE
+#error CONFIG_CHIP_INIT_ROM_REGION requires CONFIG_RO_ROM_RESIDENT_SIZE
+#endif
+
+#ifndef CONFIG_RW_ROM_RESIDENT_SIZE
+#error CONFIG_CHIP_INIT_ROM_REGION requires CONFIG_RW_ROM_RESIDENT_SIZE
+#endif
+
+
+#if (CONFIG_RO_ROM_RESIDENT_SIZE == 0)
+#error CONFIG_RO_ROM_RESIDENT_SIZE is 0 with CONFIG_CHIP_INIT_ROM_REGION defined
+#endif
+
+#if (CONFIG_RW_ROM_RESIDENT_SIZE == 0)
+#error CONFIG_RW_ROM_RESIDENT_SIZE is 0 with CONFIG_CHIP_INIT_ROM_REGION defined
+#endif
+
+#endif /* CONFIG_CHIP_INIT_ROM_REGION */
+
 /*****************************************************************************/
 
 /*