No function to enable I2C slave (STM32F0)

[riban-bw]

I am using libopencm3 with a STM32F072 as a I2C target (slave). This code block enables this mode:

// Configure GPIO B6 (I2C1 SCL), B7 (I2C1 SDA)
rcc_periph_clock_enable(RCC_GPIOB);
gpio_mode_setup(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO6);
gpio_set_af(GPIOB, GPIO_AF1, GPIO6);
gpio_mode_setup(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO7);
gpio_set_af(GPIOB, GPIO_AF1, GPIO7);

// Configure I2C1
nvic_enable_irq(NVIC_I2C1_IRQ);
i2c_reset(I2C1);
i2c_peripheral_disable(I2C1);
rcc_periph_clock_enable(RCC_I2C1);
rcc_set_i2c_clock_hsi(I2C1);
i2c_set_speed(I2C1, i2c_speed_sm_100k, 8);
i2c_set_own_7bit_slave_address(I2C1, address);
i2c_enable_interrupt(I2C1, I2C_CR1_ADDRIE);
I2C_OAR1(I2C1) |= I2C_OAR1_OA1EN_ENABLE; //!@todo This should be available in cm3 lib
i2c_peripheral_enable(I2C1);

I have to manually set the OA1EN flag in OAR1. There should be a method of enabling this mode without resorting to direct register manipulation. (That is of course the purpose of this abstraction library.) This could be done automatically when setting slave address or, maybe that could be undesirable in which case a separate function to enable slave may be desirable.