The datasheets for all the fan53555 variants (and clones using the same
interface) define so called soft start times, from enabling the regulator
until at least some percentage of the output (i.e. 92% for the rk860x
types) are available.

The regulator framework supports this with the enable_time property
but currently the fan53555 driver does not define enable_times for any
variant.

I ran into a problem with this while testing the new driver for the
Rockchip NPUs (rocket), which does runtime-pm including disabling and
enabling a rk8602 as needed. When reenabling the regulator while running
a load, fatal hangs could be observed while enabling the associated
power-domain, which the regulator supplies.

Experimentally setting the regulator to always-on, made the issue
disappear, leading to the missing delay to let power stabilize.
And as expected, setting the enable-time to a non-zero value
according to the datasheet also resolved the regulator-issue.

The datasheets in nearly all cases only specify "typical" values,
except for the fan53555 type 08. There both a typical and maximum
value are listed - 40uS apart.

For all typical values I've added 100uS to be on the safe side.
Individual details for the relevant regulators below:

- fan53526:
  The datasheet for all variants lists a typical value of 150uS, so
  make that 250uS with safety margin.
- fan53555:
  types 08 and 18 (unsupported) are given a typical enable time of 135uS
  but also a maximum of 175uS so use that value. All the other types only
  have a typical time in the datasheet of 300uS, so give a bit margin by
  setting it to 400uS.
- rk8600 + rk8602:
  Datasheet reports a typical value of 260us, so use 360uS to be safe.
- syr82x + syr83x:
  All datasheets report typical soft-start values of 300uS for these
  regulators, so use 400uS.
- tcs452x:
  Datasheet sadly does not report a soft-start time, so I've not set
  an enable-time

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
I've started with just setting regulator-enable-ramp-delay in devicetree,
but Chen-Yu suggested [0] that these are characteristics of the regulator
so possibly should be defined in the driver instead.
And after thinking about it more, I agree.

[0] https://lore.kernel.org/linux-rockchip/CAGb2v65C0jHsD2HD_AEt+AGqMfWUUwwWV0bXw4i9Hw2tCNHZpA@mail.gmail.com/

 drivers/regulator/fan53555.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/regulator/fan53555.c b/drivers/regulator/fan53555.c
index bd9447dac596..c282236959b1 100644
--- a/drivers/regulator/fan53555.c
+++ b/drivers/regulator/fan53555.c
@@ -147,6 +147,7 @@ struct fan53555_device_info {
 	unsigned int slew_mask;
 	const unsigned int *ramp_delay_table;
 	unsigned int n_ramp_values;
+	unsigned int enable_time;
 	unsigned int slew_rate;
 };
 
@@ -282,6 +283,7 @@ static int fan53526_voltages_setup_fairchild(struct fan53555_device_info *di)
 	di->slew_mask = CTL_SLEW_MASK;
 	di->ramp_delay_table = slew_rates;
 	di->n_ramp_values = ARRAY_SIZE(slew_rates);
+	di->enable_time = 250;
 	di->vsel_count = FAN53526_NVOLTAGES;
 
 	return 0;
@@ -296,10 +298,12 @@ static int fan53555_voltages_setup_fairchild(struct fan53555_device_info *di)
 		case FAN53555_CHIP_REV_00:
 			di->vsel_min = 600000;
 			di->vsel_step = 10000;
+			di->enable_time = 400;
 			break;
 		case FAN53555_CHIP_REV_13:
 			di->vsel_min = 800000;
 			di->vsel_step = 10000;
+			di->enable_time = 400;
 			break;
 		default:
 			dev_err(di->dev,
@@ -311,13 +315,19 @@ static int fan53555_voltages_setup_fairchild(struct fan53555_device_info *di)
 	case FAN53555_CHIP_ID_01:
 	case FAN53555_CHIP_ID_03:
 	case FAN53555_CHIP_ID_05:
+		di->vsel_min = 600000;
+		di->vsel_step = 10000;
+		di->enable_time = 400;
+		break;
 	case FAN53555_CHIP_ID_08:
 		di->vsel_min = 600000;
 		di->vsel_step = 10000;
+		di->enable_time = 175;
 		break;
 	case FAN53555_CHIP_ID_04:
 		di->vsel_min = 603000;
 		di->vsel_step = 12826;
+		di->enable_time = 400;
 		break;
 	default:
 		dev_err(di->dev,
@@ -350,6 +360,7 @@ static int fan53555_voltages_setup_rockchip(struct fan53555_device_info *di)
 	di->slew_mask = CTL_SLEW_MASK;
 	di->ramp_delay_table = slew_rates;
 	di->n_ramp_values = ARRAY_SIZE(slew_rates);
+	di->enable_time = 360;
 	di->vsel_count = FAN53555_NVOLTAGES;
 
 	return 0;
@@ -372,6 +383,7 @@ static int rk8602_voltages_setup_rockchip(struct fan53555_device_info *di)
 	di->slew_mask = CTL_SLEW_MASK;
 	di->ramp_delay_table = slew_rates;
 	di->n_ramp_values = ARRAY_SIZE(slew_rates);
+	di->enable_time = 360;
 	di->vsel_count = RK8602_NVOLTAGES;
 
 	return 0;
@@ -395,6 +407,7 @@ static int fan53555_voltages_setup_silergy(struct fan53555_device_info *di)
 	di->slew_mask = CTL_SLEW_MASK;
 	di->ramp_delay_table = slew_rates;
 	di->n_ramp_values = ARRAY_SIZE(slew_rates);
+	di->enable_time = 400;
 	di->vsel_count = FAN53555_NVOLTAGES;
 
 	return 0;
@@ -594,6 +607,7 @@ static int fan53555_regulator_register(struct fan53555_device_info *di,
 	rdesc->ramp_mask = di->slew_mask;
 	rdesc->ramp_delay_table = di->ramp_delay_table;
 	rdesc->n_ramp_values = di->n_ramp_values;
+	rdesc->enable_time = di->enable_time;
 	rdesc->owner = THIS_MODULE;
 
 	rdev = devm_regulator_register(di->dev, &di->desc, config);
-- 
2.47.2

On Fri, 06 Jun 2025 21:04:18 +0200, Heiko Stuebner wrote:
> The datasheets for all the fan53555 variants (and clones using the same
> interface) define so called soft start times, from enabling the regulator
> until at least some percentage of the output (i.e. 92% for the rk860x
> types) are available.
> 
> The regulator framework supports this with the enable_time property
> but currently the fan53555 driver does not define enable_times for any
> variant.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next

Thanks!

[1/1] regulator: fan53555: add enable_time support and soft-start times
      commit: 8acfb165a492251a08a22a4fa6497a131e8c2609

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

On Fri, Jun 06, 2025 at 09:04:18PM +0200, Heiko Stuebner wrote:

> I've started with just setting regulator-enable-ramp-delay in devicetree,
> but Chen-Yu suggested [0] that these are characteristics of the regulator
> so possibly should be defined in the driver instead.
> And after thinking about it more, I agree.

Yes, that's more what's expected - configuring in the DT is more for
cases where there's either configurability or board specific variation,
or for fixed voltage regulators where we don't have a compatible.