Add support for STM32L0/L1 onboard EEPROM. (#8002)

* Add support for STM32L0/L1 onboard EEPROM.

* Update docs/eeprom_driver.md

Co-Authored-By: Joel Challis <git@zvecr.com>

Co-authored-by: Joel Challis <git@zvecr.com>

4 files changed, 140 insertions, 5 deletions

diff --git a/common_features.mk b/common_features.mk
index fe65974e7a..b71dbc77e2 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -141,6 +141,10 @@ else
         SRC += $(PLATFORM_COMMON_DIR)/flash_stm32.c
         OPT_DEFS += -DEEPROM_EMU_STM32F072xB
         OPT_DEFS += -DSTM32_EEPROM_ENABLE
+      else ifneq ($(filter $(MCU_SERIES),STM32L0xx STM32L1xx),)
+        OPT_DEFS += -DEEPROM_DRIVER
+        COMMON_VPATH += $(DRIVER_PATH)/eeprom
+        SRC += eeprom_driver.c eeprom_stm32_L0_L1.c
       else
         # This will effectively work the same as "transient" if not supported by the chip
         SRC += $(PLATFORM_COMMON_DIR)/eeprom_teensy.c
diff --git a/docs/eeprom_driver.md b/docs/eeprom_driver.md
index dd12d8ec7b..5a91a7c2da 100644
--- a/docs/eeprom_driver.md
+++ b/docs/eeprom_driver.md
@@ -2,14 +2,16 @@
 
 The EEPROM driver can be swapped out depending on the needs of the keyboard, or whether extra hardware is present.
 
-Driver                      | Description
---------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-`EEPROM_DRIVER = vendor`    | Uses the on-chip driver provided by the chip manufacturer. For AVR, this is provided by avr-libc. This is supported on ARM for a subset of chips -- STM32F3xx, STM32F1xx, and STM32F072xB will be emulated by writing to flash. Other chips will generally act as "transient" below.
-`EEPROM_DRIVER = i2c`       | Supports writing to I2C-based 24xx EEPROM chips. See the driver section below.
-`EEPROM_DRIVER = transient` | Fake EEPROM driver -- supports reading/writing to RAM, and will be discarded when power is lost.
+Driver                             | Description
+-----------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+`EEPROM_DRIVER = vendor` (default) | Uses the on-chip driver provided by the chip manufacturer. For AVR, this is provided by avr-libc. This is supported on ARM for a subset of chips -- STM32F3xx, STM32F1xx, and STM32F072xB will be emulated by writing to flash. STM32L0xx and STM32L1xx will use the onboard dedicated true EEPROM. Other chips will generally act as "transient" below.
+`EEPROM_DRIVER = i2c`              | Supports writing to I2C-based 24xx EEPROM chips. See the driver section below.
+`EEPROM_DRIVER = transient`        | Fake EEPROM driver -- supports reading/writing to RAM, and will be discarded when power is lost.
 
 ## Vendor Driver Configuration
 
+!> Resetting EEPROM using an STM32L0/L1 device takes up to 1 second for every 1kB of internal EEPROM used.
+
 No configurable options are available.
 
 ## I2C Driver Configuration
diff --git a/drivers/eeprom/eeprom_stm32_L0_L1.c b/drivers/eeprom/eeprom_stm32_L0_L1.c
new file mode 100644
index 0000000000..b62e6ffd76
--- /dev/null
+++ b/drivers/eeprom/eeprom_stm32_L0_L1.c
@@ -0,0 +1,96 @@
+/* Copyright 2020 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "hal.h"
+#include "eeprom_driver.h"
+#include "eeprom_stm32_L0_L1.h"
+
+#define EEPROM_BASE_ADDR 0x08080000
+#define EEPROM_ADDR(offset) (EEPROM_BASE_ADDR + (offset))
+#define EEPROM_PTR(offset) ((__IO uint8_t *)EEPROM_ADDR(offset))
+#define EEPROM_BYTE(location, offset) (*(EEPROM_PTR(((uint32_t)location) + ((uint32_t)offset))))
+
+#define BUFFER_BYTE(buffer, offset) (*(((uint8_t *)buffer) + offset))
+
+#define FLASH_PEKEY1 0x89ABCDEF
+#define FLASH_PEKEY2 0x02030405
+
+static inline void STM32_L0_L1_EEPROM_WaitNotBusy(void) {
+    while (FLASH->SR & FLASH_SR_BSY) {
+        __WFI();
+    }
+}
+
+static inline void STM32_L0_L1_EEPROM_Unlock(void) {
+    STM32_L0_L1_EEPROM_WaitNotBusy();
+    if (FLASH->PECR & FLASH_PECR_PELOCK) {
+        FLASH->PEKEYR = FLASH_PEKEY1;
+        FLASH->PEKEYR = FLASH_PEKEY2;
+    }
+}
+
+static inline void STM32_L0_L1_EEPROM_Lock(void) {
+    STM32_L0_L1_EEPROM_WaitNotBusy();
+    FLASH->PECR |= FLASH_PECR_PELOCK;
+}
+
+void eeprom_driver_init(void) {}
+
+void eeprom_driver_erase(void) {
+    STM32_L0_L1_EEPROM_Unlock();
+
+    for (size_t offset = 0; offset < STM32_ONBOARD_EEPROM_SIZE; offset += sizeof(uint32_t)) {
+        FLASH->PECR |= FLASH_PECR_ERASE | FLASH_PECR_DATA;
+
+        *(__IO uint32_t *)EEPROM_ADDR(offset) = (uint32_t)0;
+
+        STM32_L0_L1_EEPROM_WaitNotBusy();
+        FLASH->PECR &= ~(FLASH_PECR_ERASE | FLASH_PECR_DATA);
+    }
+
+    STM32_L0_L1_EEPROM_Lock();
+}
+
+void eeprom_read_block(void *buf, const void *addr, size_t len) {
+    for (size_t offset = 0; offset < len; ++offset) {
+        // Drop out if we've hit the limit of the EEPROM
+        if ((((uint32_t)addr) + offset) >= STM32_ONBOARD_EEPROM_SIZE) {
+            break;
+        }
+
+        STM32_L0_L1_EEPROM_WaitNotBusy();
+        BUFFER_BYTE(buf, offset) = EEPROM_BYTE(addr, offset);
+    }
+}
+
+void eeprom_write_block(const void *buf, void *addr, size_t len) {
+    STM32_L0_L1_EEPROM_Unlock();
+
+    for (size_t offset = 0; offset < len; ++offset) {
+        // Drop out if we've hit the limit of the EEPROM
+        if ((((uint32_t)addr) + offset) >= STM32_ONBOARD_EEPROM_SIZE) {
+            break;
+        }
+
+        STM32_L0_L1_EEPROM_WaitNotBusy();
+        EEPROM_BYTE(addr, offset) = BUFFER_BYTE(buf, offset);
+    }
+
+    STM32_L0_L1_EEPROM_Lock();
+}
diff --git a/drivers/eeprom/eeprom_stm32_L0_L1.h b/drivers/eeprom/eeprom_stm32_L0_L1.h
new file mode 100644
index 0000000000..a35defca8b
--- /dev/null
+++ b/drivers/eeprom/eeprom_stm32_L0_L1.h
@@ -0,0 +1,33 @@
+/* Copyright 2020 Nick Brassel (tzarc)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/*
+    The size used by the STM32 L0/L1 EEPROM driver.
+*/
+#ifndef STM32_ONBOARD_EEPROM_SIZE
+#    ifdef VIA_ENABLE
+#        define STM32_ONBOARD_EEPROM_SIZE 1024
+#    else
+#        include "eeconfig.h"
+#        define STM32_ONBOARD_EEPROM_SIZE (((EECONFIG_SIZE + 3) / 4) * 4)  // based off eeconfig's current usage, aligned to 4-byte sizes, to deal with LTO and EEPROM page sizing
+#    endif
+#endif
+
+#if STM32_ONBOARD_EEPROM_SIZE > 128
+#    pragma message("Please note: resetting EEPROM using an STM32L0/L1 device takes up to 1 second for every 1kB of internal EEPROM used.")
+#endif