Save battery thresholds at second-to-last sector

Make battery thresholds persistent by saving them in flash space. This
allows configuring them after EC reset (system powered-off, unplugged)
but before any system firmware or OS policy can be applied.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/acpi.c

@@ -215,6 +215,7 @@ void acpi_write(uint8_t addr, uint8_t data) {
 
  case 0xBD:
  battery_set_end_threshold(data);
+ (void)battery_save_thresholds();
  break;
 
 #if HAVE_LED_AIRPLANE_N

src/board/system76/common/battery.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
 #include <board/battery.h>
+#include <board/flash.h>
 #include <board/gpio.h>
 #include <board/smbus.h>
 #include <common/debug.h>
@@ -13,6 +14,18 @@ uint16_t battery_charger_input_current = CHARGER_INPUT_CURRENT;
 #define BATTERY_START_DEFAULT 0
 #define BATTERY_END_DEFAULT 100
 
+// Flash address to save charging thresholds to
+static const uint32_t BAT_CFG_ADDR = CONFIG_EC_FLASH_SIZE - (2 * 1024);
+static const uint16_t BAT_CFG_MAGIC = 0x4254;
+
+struct battery_config {
+ uint16_t magic;
+ uint8_t start_threshold;
+ uint8_t end_threshold;
+};
+
+static struct battery_config __xdata bat_cfg = { { 0 } };
+
 // Represents a battery percentage level, below which charging will begin.
 // Valid values are [0, 100]
 // A value of 0 turns off the start threshold control.
@@ -112,3 +125,38 @@ void battery_reset(void) {
  battery_start_threshold = BATTERY_START_THRESHOLD;
  battery_end_threshold = BATTERY_END_THRESHOLD;
 }
+
+// Read the charge thresholds from flash. Falls back to defaults if not found.
+bool battery_load_thresholds(void) {
+ bool loaded = true;
+
+ flash_read(BAT_CFG_ADDR, (uint8_t *)&bat_cfg, sizeof(bat_cfg));
+
+ if (bat_cfg.magic != BAT_CFG_MAGIC) {
+ bat_cfg.magic = BAT_CFG_MAGIC;
+ bat_cfg.start_threshold = BATTERY_START_THRESHOLD;
+ bat_cfg.end_threshold = BATTERY_END_THRESHOLD;
+ loaded = false;
+ }
+
+ battery_start_threshold = battery_set_start_threshold(bat_cfg.start_threshold);
+ battery_end_threshold = battery_set_end_threshold(bat_cfg.end_threshold);
+
+ return loaded;
+}
+
+// Write the charge thresholds to flash.
+bool battery_save_thresholds(void) {
+ if ((bat_cfg.start_threshold == battery_start_threshold) &&
+ (bat_cfg.end_threshold == battery_end_threshold)) {
+ return true;
+ }
+
+ bat_cfg.start_threshold = battery_start_threshold;
+ bat_cfg.end_threshold = battery_end_threshold;
+
+ flash_erase(BAT_CFG_ADDR);
+ flash_write(BAT_CFG_ADDR, (uint8_t *)&bat_cfg, sizeof(bat_cfg));
+
+ return flash_read_u16(BAT_CFG_ADDR) == BAT_CFG_MAGIC;
+}

src/board/system76/common/include/board/battery.h

@@ -43,6 +43,9 @@ bool battery_set_start_threshold(uint8_t value);
 uint8_t battery_get_end_threshold(void);
 bool battery_set_end_threshold(uint8_t value);
 
+bool battery_load_thresholds(void);
+bool battery_save_thresholds(void);
+
 int16_t battery_charger_configure(void);
 void battery_event(void);
 void battery_reset(void);

src/board/system76/common/main.c

@@ -85,6 +85,7 @@ void init(void) {
  // Must happen last
  power_init();
  board_init();
+ battery_load_thresholds();
 }
 
 void main(void) {