diff --git a/src/arch/avr/gpio.c b/src/arch/avr/gpio.c
index e4cefa2..c11e7ce 100644
--- a/src/arch/avr/gpio.c
+++ b/src/arch/avr/gpio.c
@@ -2,7 +2,7 @@
 
 #include <arch/gpio.h>
 
-bool gpio_get_dir(struct Gpio *const gpio) {
+bool gpio_get_dir(const struct Gpio *const gpio) {
     if (*gpio->ddr & gpio->value) {
         return true;
     } else {
@@ -18,7 +18,7 @@ void gpio_set_dir(struct Gpio *const gpio, bool value) {
     }
 }
 
-bool gpio_get(struct Gpio *const gpio) {
+bool gpio_get(const struct Gpio *const gpio) {
     if (*gpio->pin & gpio->value) {
         return true;
     } else {
diff --git a/src/arch/avr/i2c.c b/src/arch/avr/i2c.c
index 02a203d..502c5bf 100644
--- a/src/arch/avr/i2c.c
+++ b/src/arch/avr/i2c.c
@@ -52,7 +52,7 @@ void i2c_stop(struct I2C *const i2c) {
     TWCR = BIT(TWINT) | BIT(TWEN) | BIT(TWSTO);
 }
 
-int16_t i2c_write(struct I2C *const i2c, uint8_t *const data, uint16_t length) {
+int16_t i2c_write(struct I2C *const i2c, const uint8_t *const data, uint16_t length) {
     uint16_t i;
     for (i = 0; i < length; i++) {
         // load data into data register
diff --git a/src/arch/avr/include/arch/gpio.h b/src/arch/avr/include/arch/gpio.h
index 95c68a3..ca5f77a 100644
--- a/src/arch/avr/include/arch/gpio.h
+++ b/src/arch/avr/include/arch/gpio.h
@@ -25,9 +25,9 @@ struct Gpio {
 }
 // clang-format on
 
-bool gpio_get(struct Gpio *const gpio);
+bool gpio_get(const struct Gpio *const gpio);
 void gpio_set(struct Gpio *const gpio, bool value);
-bool gpio_get_dir(struct Gpio *const gpio);
+bool gpio_get_dir(const struct Gpio *const gpio);
 void gpio_set_dir(struct Gpio *const gpio, bool value);
 
 #endif // _ARCH_GPIO_H
diff --git a/src/board/arduino/mega2560/parallel.c b/src/board/arduino/mega2560/parallel.c
index 7f0f496..215ae31 100644
--- a/src/board/arduino/mega2560/parallel.c
+++ b/src/board/arduino/mega2560/parallel.c
@@ -436,7 +436,7 @@ int16_t parallel_spi_transaction(
 // "Hardware" accelerated SPI programming, requires ECINDARs to be set
 int16_t parallel_spi_program(
     struct Parallel *const port,
-    uint8_t *const data,
+    const uint8_t *const data,
     int16_t length,
     bool initialized
 ) {
diff --git a/src/board/arduino/uno/parallel.c b/src/board/arduino/uno/parallel.c
index da87e2c..e853f31 100644
--- a/src/board/arduino/uno/parallel.c
+++ b/src/board/arduino/uno/parallel.c
@@ -346,7 +346,7 @@ int16_t parallel_spi_transaction(
 // "Hardware" accelerated SPI programming, requires ECINDARs to be set
 int16_t parallel_spi_program(
     struct Parallel *const port,
-    uint8_t *const data,
+    const uint8_t *const data,
     int16_t length,
     bool initialized
 ) {
diff --git a/src/board/system76/common/include/board/parallel.h b/src/board/system76/common/include/board/parallel.h
index 674b10a..7f075ee 100644
--- a/src/board/system76/common/include/board/parallel.h
+++ b/src/board/system76/common/include/board/parallel.h
@@ -8,6 +8,6 @@
 
 extern bool parallel_debug;
 bool parallel_init(void);
-int16_t parallel_write(uint8_t *const data, uint16_t length);
+int16_t parallel_write(const uint8_t *const data, uint16_t length);
 
 #endif // _BOARD_PARALLEL_H
diff --git a/src/board/system76/common/kbc.c b/src/board/system76/common/kbc.c
index 6222daa..50f3715 100644
--- a/src/board/system76/common/kbc.c
+++ b/src/board/system76/common/kbc.c
@@ -92,7 +92,7 @@ static bool kbc_buffer_pop(uint8_t *const scancode) {
     return true;
 }
 
-static bool kbc_buffer_push(uint8_t *const scancodes, uint8_t len) {
+static bool kbc_buffer_push(const uint8_t *const scancodes, uint8_t len) {
     //TODO: make this test more efficient
     for (uint8_t i = 0; i < len; i++) {
         if ((kbc_buffer_tail + i + 1U) % ARRAY_SIZE(kbc_buffer) == kbc_buffer_head) {
diff --git a/src/board/system76/common/kbscan.c b/src/board/system76/common/kbscan.c
index 2ac1b4b..b3e33b2 100644
--- a/src/board/system76/common/kbscan.c
+++ b/src/board/system76/common/kbscan.c
@@ -96,7 +96,7 @@ static inline bool popcount_more_than_one(uint8_t rowdata) {
     return rowdata & (rowdata - 1);
 }
 
-static bool kbscan_row_has_ghost(uint8_t *const matrix, uint8_t col) {
+static bool kbscan_row_has_ghost(const uint8_t *const matrix, uint8_t col) {
     uint8_t rowdata = matrix[col];
 
     // No ghosts exist when less than 2 keys in the row are active.
diff --git a/src/board/system76/common/parallel.c b/src/board/system76/common/parallel.c
index de50131..6476c4f 100644
--- a/src/board/system76/common/parallel.c
+++ b/src/board/system76/common/parallel.c
@@ -84,7 +84,7 @@ bool parallel_init(void) {
     return parallel_wait_peripheral(STS_WAIT, 0);
 }
 
-int16_t parallel_write(uint8_t *const data, uint16_t length) {
+int16_t parallel_write(const uint8_t *const data, uint16_t length) {
     // Assert nWRITE
     KSIGDAT &= ~CTL_WRITE;
 
diff --git a/src/common/include/common/i2c.h b/src/common/include/common/i2c.h
index 8288a0f..87bbd6b 100644
--- a/src/common/include/common/i2c.h
+++ b/src/common/include/common/i2c.h
@@ -24,7 +24,7 @@ void i2c_stop(struct I2C *const i2c) __reentrant;
 
 // Send a byte on i2c bus
 // Must be defined by arch, board, or ec
-int16_t i2c_write(struct I2C *const i2c, uint8_t *const data, uint16_t length) __reentrant;
+int16_t i2c_write(struct I2C *const i2c, const uint8_t *const data, uint16_t length) __reentrant;
 
 // Read bytes from bus
 // Must be defined by arch, board, or ec
diff --git a/src/ec/ite/gpio.c b/src/ec/ite/gpio.c
index b46852f..8eaee98 100644
--- a/src/ec/ite/gpio.c
+++ b/src/ec/ite/gpio.c
@@ -3,7 +3,7 @@
 #include <ec/gpio.h>
 #include <common/debug.h>
 
-bool gpio_get(struct Gpio *const gpio) {
+bool gpio_get(const struct Gpio *const gpio) {
     if (*(gpio->data) & gpio->value) {
         return true;
     } else {
diff --git a/src/ec/ite/include/ec/gpio.h b/src/ec/ite/include/ec/gpio.h
index 02370ee..8debc8d 100644
--- a/src/ec/ite/include/ec/gpio.h
+++ b/src/ec/ite/include/ec/gpio.h
@@ -32,7 +32,7 @@ struct Gpio {
 }
 // clang-format on
 
-bool gpio_get(struct Gpio *const gpio);
+bool gpio_get(const struct Gpio *const gpio);
 void gpio_set(struct Gpio *const gpio, bool value);
 
 #ifdef GPIO_DEBUG
diff --git a/src/ec/ite/include/ec/kbc.h b/src/ec/ite/include/ec/kbc.h
index e005d15..0fbc254 100644
--- a/src/ec/ite/include/ec/kbc.h
+++ b/src/ec/ite/include/ec/kbc.h
@@ -29,8 +29,8 @@ extern struct Kbc __code KBC;
 #define KBC_STS_IBF BIT(1)
 #define KBC_STS_CMD BIT(3)
 
-uint8_t kbc_status(struct Kbc *const kbc);
-uint8_t kbc_read(struct Kbc *const kbc);
+uint8_t kbc_status(const struct Kbc *const kbc);
+uint8_t kbc_read(const struct Kbc *const kbc);
 bool kbc_keyboard(struct Kbc *const kbc, uint8_t data, uint16_t timeout);
 bool kbc_mouse(struct Kbc *const kbc, uint8_t data, uint16_t timeout);
 
diff --git a/src/ec/ite/kbc.c b/src/ec/ite/kbc.c
index d856b4f..5fd6349 100644
--- a/src/ec/ite/kbc.c
+++ b/src/ec/ite/kbc.c
@@ -12,15 +12,15 @@ struct Kbc __code KBC = {
     .data_in = &KBHIDIR,
 };
 
-uint8_t kbc_status(struct Kbc *const kbc) {
+uint8_t kbc_status(const struct Kbc *const kbc) {
     return *(kbc->status);
 }
 
-uint8_t kbc_read(struct Kbc *const kbc) {
+uint8_t kbc_read(const struct Kbc *const kbc) {
     return *(kbc->data_in);
 }
 
-static bool kbc_wait(struct Kbc *const kbc, uint16_t timeout) {
+static bool kbc_wait(const struct Kbc *const kbc, uint16_t timeout) {
     while (*(kbc->status) & KBC_STS_OBF) {
         if (timeout == 0)
             return false;