Bug in the bq769x2_set_switches

[vlebedev-ora]

bms-firmware/drivers/bms_ic/bq769x2/bq769x2.c

Lines 833 to 861 in 8f6a949

	err = bq769x2_direct_read_u1(dev, BQ769X2_CMD_FET_STATUS, &fet_status.byte);
	if (err != 0) {
	return err;
	}
	/* only lower 4 bytes relevant for FET_CONTROL */
	fet_status.byte &= 0x0F;
	if (switches & BMS_SWITCH_CHG) {
	fet_status.CHG_FET = enabled ? 1 : 0;
	}
	if (switches & BMS_SWITCH_DIS) {
	fet_status.DSG_FET = enabled ? 1 : 0;
	}
	if (switches & BMS_SWITCH_PDSG) {
	fet_status.PDSG_FET = enabled ? 1 : 0;
	}
	if (switches & BMS_SWITCH_PCHG) {
	fet_status.PCHG_FET = enabled ? 1 : 0;
	}
	err = bq769x2_subcmd_write_u1(dev, BQ769X2_SUBCMD_FET_CONTROL, fet_status.byte);
	if (enabled) {
	err |= bq769x2_subcmd_cmd_only(dev, BQ769X2_SUBCMD_ALL_FETS_ON);
	}
	return err == 0 ? 0 : -EIO;
	}

The code he assumes that the FET CONTROL subcommand argument is organized the same way as FET STATUS
register. This assumption is WRONG - the argument is organized as FET CONTROL register!!!!

See:
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1453973/bq76952-possible-error-in-technical-reference-manual-concerning-fet-control/5577692#5577692

[vlebedev-ora]

To handle this problem we did the following:

1. We defined the SWITCH flags to match FET_CONTROL register

#define BQ769x2_SWITCH_DSG (1 << 0)
#define BQ769x2_SWITCH_PDSG (1 << 1)
#define BQ769x2_SWITCH_CHG (1 << 2)
#define BQ769x2_SWITCH_PCHG (1 << 3)

2. We created function:

/**
 * @brief Switch the specified MOSFET(s) on (Non specified will be blocked).
 *
 * @param dev Pointer to the device structure for the driver instance.
 * @param switches MOSFET(s) to switch on (See BQ769x2_SWITCH_*).
 *
 * @return 0 for success or negative error code otherwise.
 */
BQ769x2_API int bq769x2_enable_switches(const struct bq769x2 *dev,
					uint8_t switches)
{
	uint8_t fet_control;
	int err;

	fet_control = ~switches & 0x0f;

	err = bq769x2_subcmd_write_u1(dev, BQ769X2_SUBCMD_FET_CONTROL,
				      fet_control);

	return err == 0 ? 0 : -EIO;
}