From c5cf53b690a40f3c92723c69acb18843371a567c Mon Sep 17 00:00:00 2001
From: Tim Lin <tim2.lin@ite.corp-partner.google.com>
Date: Mon, 24 Jun 2024 11:52:03 +0800
Subject: [PATCH] soc: it8xxx2: linker: Move serial library to RAM to enhance
 performance

Place serial library in ILM. This can improve performance.

test:
Print the message 10000 times with 1ms sleep interval to compare the
time difference before and after adding RAM code on the it82002bw evb.

                         RAM code size    save time
original:                1954 bytes
libdrivers__serial.a:   +2282 bytes      -226ms

Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>
---
 soc/ite/ec/it8xxx2/Kconfig   | 14 ++++++++++++++
 soc/ite/ec/it8xxx2/linker.ld | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/soc/ite/ec/it8xxx2/Kconfig b/soc/ite/ec/it8xxx2/Kconfig
index 38b92c9c6b8..2dfe2d5afc9 100644
--- a/soc/ite/ec/it8xxx2/Kconfig
+++ b/soc/ite/ec/it8xxx2/Kconfig
@@ -183,6 +183,20 @@ config SOC_IT8XXX2_EXCEPTIONS_IN_RAM
 	  Flash. This can significantly improve performance when under I-cache
 	  pressure.
 
+config SOC_IT8XXX2_LIBRARY_TO_RAM
+	bool
+	help
+	  If this is selected it means that there is a library that needs to be excluded
+	  from the text section.
+
+config SOC_IT8XXX2_SERIAL_IN_RAM
+	bool "Place serial handling code in RAM"
+	select SOC_IT8XXX2_USE_ILM
+	select SOC_IT8XXX2_LIBRARY_TO_RAM
+	help
+	  Place serial handling (Include uart_ns16550.c and uart_ite_it8xxx2.c) code
+	  in ILM. This can improve performance.
+
 config SOC_IT8XXX2_SHA256_HW_ACCELERATE
 	bool "HW SHA256 calculation"
 	help
diff --git a/soc/ite/ec/it8xxx2/linker.ld b/soc/ite/ec/it8xxx2/linker.ld
index a40c97dc3f2..0c4e3d483dd 100644
--- a/soc/ite/ec/it8xxx2/linker.ld
+++ b/soc/ite/ec/it8xxx2/linker.ld
@@ -165,9 +165,34 @@ SECTIONS
 		KEEP(*(".openocd_debug.*"))
 
 		__text_region_start = .;
-
+#ifndef CONFIG_SOC_IT8XXX2_LIBRARY_TO_RAM
 		*(.text)
 		*(".text.*")
+#endif
+
+#ifdef CONFIG_SOC_IT8XXX2_LIBRARY_TO_RAM
+		*(EXCLUDE_FILE (
+#endif
+#ifdef CONFIG_SOC_IT8XXX2_SERIAL_IN_RAM
+			*libdrivers__serial.a:*
+#endif
+#ifdef CONFIG_SOC_IT8XXX2_LIBRARY_TO_RAM
+		)
+			.text
+		)
+#endif
+
+#ifdef CONFIG_SOC_IT8XXX2_LIBRARY_TO_RAM
+		*(EXCLUDE_FILE (
+#endif
+#ifdef CONFIG_SOC_IT8XXX2_SERIAL_IN_RAM
+			*libdrivers__serial.a:*
+#endif
+#ifdef CONFIG_SOC_IT8XXX2_LIBRARY_TO_RAM
+		)
+			.text.*
+		)
+#endif
 		*(.gnu.linkonce.t.*)
 #include <zephyr/linker/kobject-text.ld>
 
@@ -189,6 +214,11 @@ SECTIONS
 #ifdef CONFIG_SOC_IT8XXX2_EXCEPTIONS_IN_RAM
 		KEEP(*(".exception.entry.*"))
 		*(".exception.other.*")
+#endif
+#ifdef CONFIG_SOC_IT8XXX2_SERIAL_IN_RAM
+		*libdrivers__serial.a:*(.text .text.*)
+		*libdrivers__serial.a:*(.rodata .rodata.*)
+		*libdrivers__serial.a:*(.srodata .srodata.*)
 #endif
 		__ilm_flash_end = .;
 		/* ILM mapping is always a multiple of 4k size; ensure following