Re: [PATCH 4/6] ARM: i.MX8MP: skov: halt startup until power is good

[Marco Felsch <m.felsch@pengutronix.de>]

Hi,

On 25-04-14, Ahmad Fatoum wrote:
> The 24V regulator supplying the system can indicate via a GPIO imminent
> voltage loss. The board's capacitors hold enough charge to power the system
> a while longer in such a state, but eventually, unless external power is
> restored, the brownout detection of the PMIC will kick in.
> 
> For the span of time between voltage drop detection and PMIC brownout,
> let's detect this situation and delay startup. This way, Linux can
> detect the ongoing voltage loss, power down the eMMC, reboot into
> barebox and barebox will delay boot as long as the problem persists.
> 
> Co-developed-by: Kim Christensen <kch@skov.dk>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  arch/arm/boards/skov-imx8mp/lowlevel.c | 60 ++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
> 
> diff --git a/arch/arm/boards/skov-imx8mp/lowlevel.c b/arch/arm/boards/skov-imx8mp/lowlevel.c
> index 637fc50b3f30..d7bd771f259d 100644
> --- a/arch/arm/boards/skov-imx8mp/lowlevel.c
> +++ b/arch/arm/boards/skov-imx8mp/lowlevel.c
> @@ -20,6 +20,9 @@
>  
>  extern char __dtb_z_imx8mp_skov_start[];
>  
> +#define PGOOD_PAD_CTRL  MUX_PAD_CTRL(MX8MP_PAD_CTL_PUE | \
> +				     MX8MP_PAD_CTL_PE)
> +
>  #define UART_PAD_CTRL   MUX_PAD_CTRL(MX8MP_PAD_CTL_DSE6 | \
>  				     MX8MP_PAD_CTL_FSEL | \
>  				     MX8MP_PAD_CTL_PUE | \
> @@ -30,6 +33,12 @@ extern char __dtb_z_imx8mp_skov_start[];
>  				     MX8MP_PAD_CTL_PUE | \
>  				     MX8MP_PAD_CTL_PE)
>  
> +static inline void led_d1_toggle(bool *on)
> +{
> +	imx8m_gpio_direction_output(IOMEM(MX8MP_GPIO1_BASE_ADDR), 5, *on);
> +	*on = !*on;
> +}
> +
>  static void setup_uart(void)
>  {
>  	void __iomem *uart = IOMEM(MX8M_UART2_BASE_ADDR);
> @@ -67,6 +76,55 @@ static struct pmic_config pca9450_cfg[] = {
>  	{ PCA9450_BUCK2OUT_DVS0, 0x14 },
>  };
>  
> +static inline bool power_good(void)
> +{
> +	/* IMX_SHDN_MF in schematics */
> +	return imx8m_gpio_val(IOMEM(MX8MP_GPIO4_BASE_ADDR), 23);
> +}
> +
> +static void wait_for_power_good(void)
> +{
> +	void __iomem *gpio4 = IOMEM(MX8MP_GPIO4_BASE_ADDR);
> +	int timeout_ms = 0;
> +	bool led_active = true;
> +
> +	imx8mp_setup_pad(MX8MP_PAD_SAI2_RXD0__GPIO4_IO23 | PGOOD_PAD_CTRL);
> +	imx8m_gpio_direction_input(gpio4, 23);
> +
> +	led_d1_toggle(&led_active);
> +
> +	if (power_good())
> +		return;
> +
> +	pr_warn("\nDelaying boot until power stabilizes\n");
> +
> +	/* If we reach this, because Linux did a hw_protection_reboot, we don't
> +	 * want to continue booting right away.
> +	 *
> +	 * Thus let's either wait for the condition to subscede or for voltage
> +	 * to reach a low enough level for the PMIC to detect VSYS_UVLO going
> +	 * lower than allowed
> +	 */
> +
> +	while (1) {
> +		if (power_good()) {
> +			/* wait 10ms longer and check if it still good */
> +			udelay(10000);
> +			if (power_good()) {
> +				pr_info("IMX_SHDN_MF stuck low for ~%ums.\n", timeout_ms);
> +				break;
> +			}
> +		}
> +		/* fast blink LED D1 */
> +		if (timeout_ms % 100 == 0) {
> +			pr_debug(".");
> +			led_d1_toggle(&led_active);
> +		}
> +		udelay(1000);
> +		timeout_ms++;
> +	}
> +}
> +
>  static void power_init_board(void)
>  {
>  	struct pbl_i2c *i2c;
> @@ -77,6 +135,8 @@ static void power_init_board(void)
>  	imx8mp_setup_pad(MX8MP_PAD_SAI3_TXD__GPIO5_IO01);
>  	imx8m_gpio_direction_output(IOMEM(MX8MP_GPIO5_BASE_ADDR), 1, 0);
>  
> +	wait_for_power_good();

out of curiosity, wouldn't it be more useful to do the check right
before the system wants to boot the kernel and abort in that case?

Regards,
  Marco


> +
>  	imx8mp_setup_pad(MX8MP_PAD_I2C1_SCL__I2C1_SCL | I2C_PAD_CTRL);
>  	imx8mp_setup_pad(MX8MP_PAD_I2C1_SDA__I2C1_SDA | I2C_PAD_CTRL);
>  
> -- 
> 2.39.5
> 
> 
>