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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Marco,

On 14.04.25 10:40, Marco Felsch wrote:
> 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?

How so?

When we have brownout, we usually never make it out of the PBL,
so I prefer the SoC gets powered off during this loop instead
of during the RAM setup.

Cheers,
ahmad

> 
> 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
>>
>>
>>
> 


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