On 25-04-14, Ahmad Fatoum wrote:
> Hello Marco,
>
> On 14.04.25 11:21, Marco Felsch wrote:
> > On 25-04-14, Ahmad Fatoum wrote:
> >> 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 <k...@skov.dk>
> >>>> Signed-off-by: Ahmad Fatoum <a.fat...@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,
> >
> > Okay, since your backup charge is really low already.
> >
> >> so I prefer the SoC gets powered off during this loop instead
> >> of during the RAM setup.
> >
> > I understand that to wait for the power to become good again, but what
> > if the power is getting good and changes to bad again once you entered
> > barebox? Do you get notified about such an event?
> >
> > IMHO the later point a bit more important since this ensures that the
> > system was in power-good state before we the system starts.
>
> Checking just before booting is insufficient anyway, because power good
> may fluctuate before the Linux driver starts taking care of the power
> good GPIO. Given that we need to handle this anyway, I don't think
> it makes much difference whether when we check the power good GPIO
> during barebox runtime.
I know, but still it is good to check and to wait for power-good state
before you cont. booting. Like you do for barebox: you wait till the
power is good or die within the PBL.
Regards,
Marco
>
> Cheers,
> Ahmad
>
> >
> > Regards,
> > Marco
> >
>
>
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