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>
Link: https://patch.msgid.link/20250606190418.478633-1-heiko@sntech.de
Signed-off-by: Mark Brown <broonie@kernel.org>
