cortex-m: enable I-cache on ARMv7-M

The ARMv7-M ISA defines standard (and optional) mechanism to manage the
CPU caches through the SCB (System Control Block) registers.
So far, only the Cortex-M7 core implements such as a mechanism (e.g. the
Cortex-M4 with caches we have are using a proprietary mechanism for the
management).

Define the functions to use the I-Cache,
and enable them on STM32H7 which is our only supported Cortex-M7 core.

The D-Cache mechanism is still To Be Done, as it involves a bit more
support in the firmware for the DMA memory areas.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=b:67081508
TEST=on ZerbleBarn, verify manually that the 'IC' bit is set in the CCR
(e.g. 'rw 0xe000ed14' returns 0x60218), and runs some CPU workload
without crash and with a speed-up.

Change-Id: I6af1021d65048b787630387f7d95797db15d069c
Reviewed-on: https://chromium-review.googlesource.com/943445
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>

5 files changed, 61 insertions, 0 deletions

diff --git a/chip/stm32/config-stm32h7x3.h b/chip/stm32/config-stm32h7x3.h
index 72b9bd21de..4fde40b957 100644
--- a/chip/stm32/config-stm32h7x3.h
+++ b/chip/stm32/config-stm32h7x3.h
@@ -59,3 +59,6 @@
 
 /* Number of IRQ vectors on the NVIC */
 #define CONFIG_IRQ_COUNT	150
+
+/* the Cortex-M7 core has 'standard' ARMv7-M caches */
+#define CONFIG_ARMV7M_CACHE
diff --git a/chip/stm32/system.c b/chip/stm32/system.c
index 4a5927d90c..d2c48cdc11 100644
--- a/chip/stm32/system.c
+++ b/chip/stm32/system.c
@@ -205,6 +205,10 @@ void chip_pre_init(void)
 	uint32_t apb1fz_reg = 0;
 	uint32_t apb2fz_reg = 0;
 
+#ifdef CONFIG_ARMV7M_CACHE
+	cpu_enable_icache();
+#endif
+
 #if defined(CHIP_FAMILY_STM32F0)
 	apb1fz_reg =
 		STM32_RCC_PB1_TIM2 | STM32_RCC_PB1_TIM3 | STM32_RCC_PB1_TIM6 |
diff --git a/core/cortex-m/cpu.c b/core/cortex-m/cpu.c
index 2571a4a17c..ea6cf5c4a5 100644
--- a/core/cortex-m/cpu.c
+++ b/core/cortex-m/cpu.c
@@ -5,7 +5,9 @@
  * Set up the Cortex-M core
  */
 
+#include "common.h"
 #include "cpu.h"
+#include "hooks.h"
 
 void cpu_init(void)
 {
@@ -16,3 +18,39 @@ void cpu_init(void)
 	CPU_NVIC_SHCSR |= CPU_NVIC_SHCSR_MEMFAULTENA |
 		CPU_NVIC_SHCSR_BUSFAULTENA | CPU_NVIC_SHCSR_USGFAULTENA;
 }
+
+#ifdef CONFIG_ARMV7M_CACHE
+static void cpu_invalidate_icache(void)
+{
+	/*
+	 * Invalidates the entire instruction cache to the point of
+	 * unification.
+	 */
+	CPU_SCB_ICIALLU = 0;
+	asm volatile("dsb; isb");
+}
+
+void cpu_enable_icache(void)
+{
+	/* Check whether the I-cache is already enabled */
+	if (!(CPU_NVIC_CCR & CPU_NVIC_CCR_ICACHE)) {
+		/* Invalidate the I-cache first */
+		cpu_invalidate_icache();
+		/* Turn on the caching */
+		CPU_NVIC_CCR |= CPU_NVIC_CCR_ICACHE;
+		asm volatile("dsb; isb");
+	}
+}
+
+static void cpu_sysjump_cache(void)
+{
+	/*
+	 * Disable the I-cache
+	 * so we will invalidate it after the sysjump if needed
+	 * (e.g after a flash update).
+	 */
+	CPU_NVIC_CCR &= ~CPU_NVIC_CCR_ICACHE;
+	asm volatile("dsb; isb");
+}
+DECLARE_HOOK(HOOK_SYSJUMP, cpu_sysjump_cache, HOOK_PRIO_LAST);
+#endif /* CONFIG_ARMV7M_CACHE */
diff --git a/core/cortex-m/cpu.h b/core/cortex-m/cpu.h
index 07e1c4b543..f4400a0444 100644
--- a/core/cortex-m/cpu.h
+++ b/core/cortex-m/cpu.h
@@ -41,6 +41,8 @@ enum {
 	CPU_NVIC_MMFS_BFARVALID		= 1 << 15,
 	CPU_NVIC_MMFS_MFARVALID		= 1 << 7,
 
+	CPU_NVIC_CCR_ICACHE		= 1 << 17,
+	CPU_NVIC_CCR_DCACHE		= 1 << 16,
 	CPU_NVIC_CCR_DIV_0_TRAP		= 1 << 4,
 	CPU_NVIC_CCR_UNALIGN_TRAP	= 1 << 3,
 
@@ -53,7 +55,15 @@ enum {
 	CPU_NVIC_SHCSR_USGFAULTENA	= 1 << 18,
 };
 
+/* System Control Block: cache registers */
+#define CPU_SCB_CCSIDR         CPUREG(0xe000ed80)
+#define CPU_SCB_CCSELR         CPUREG(0xe000ed84)
+#define CPU_SCB_ICIALLU        CPUREG(0xe000ef50)
+#define CPU_SCB_DCISW          CPUREG(0xe000ef60)
+
 /* Set up the cpu to detect faults */
 void cpu_init(void);
+/* Enable the CPU instruction cache if it is not already enabled */
+void cpu_enable_icache(void);
 
 #endif /* __CROS_EC_CPU_H */
diff --git a/include/config.h b/include/config.h
index 8d023c54ba..bdf40ec722 100644
--- a/include/config.h
+++ b/include/config.h
@@ -187,6 +187,12 @@
 /* Support AP Warm reset Interrupt. */
 #undef CONFIG_AP_WARM_RESET_INTERRUPT
 
+/*
+ * Enable support for CPU caches behaving according to the ARMv7-M ISA.
+ * (so far, only the Cortex-M7 has such caches)
+ */
+#undef CONFIG_ARMV7M_CACHE
+
 /* Allow proprietary communication protocols' extensions. */
 #undef CONFIG_EXTENSION_COMMAND