linux-kernel - Re: [PATCH v2] regulator: qcom-rpmh: Add support for regulator-off-on-delay-us

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Message-ID: <CAAFDt1tuod0GUepTuKYN3xM1pGHTLt0tkpQpE1=ySGBsNsoiFA@mail.gmail.com>
Date: Wed, 28 Jan 2026 17:04:36 +0530
From: Saikiran B <bjsaikiran@...il.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: broonie@...nel.org, lgirdwood@...il.com, andersson@...nel.org, 
	konrad.dybcio@...nel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] regulator: qcom-rpmh: Add support for regulator-off-on-delay-us

On Wed, Jan 28, 2026 at 4:00 PM Konrad Dybcio
<konrad.dybcio@....qualcomm.com> wrote:
>
> On 1/27/26 6:37 PM, Saikiran wrote:
> > The core regulator framework supports enforcing a physical off-time via
> > standard properties, but the `qcom-rpmh-regulator` driver currently ignores
> > them. This prevents boards with slow-discharging rails from enforcing safe
> > power-cycling constraints.
> >
> > On the Lenovo Yoga Slim 7x (Snapdragon X Elite), certain camera regulators
> > rely on passive discharge and require a significant off-time to drop below
> > brownout thresholds. Without this driver support, we cannot enforce this
> > constraint via Device Tree, leading to sensor initialization failures during
> > rapid power cycling.
> >
> > Add support for parsing the `regulator-off-on-delay-us` property from
> > the device tree.
> >
> > I have tested this on the Yoga Slim 7x. When the delay property is present
> > in the device tree, the regulator core correctly blocks re-enable calls
> > until the delay passes, fixing the camera brownout issues.
> >
> > Signed-off-by: Saikiran <bjsaikiran@...il.com>
> > ---
> >  drivers/regulator/qcom-rpmh-regulator.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/regulator/qcom-rpmh-regulator.c b/drivers/regulator/qcom-rpmh-regulator.c
> > index 6e4cb2871fca..aafba61551b3 100644
> > --- a/drivers/regulator/qcom-rpmh-regulator.c
> > +++ b/drivers/regulator/qcom-rpmh-regulator.c
> > @@ -503,6 +503,9 @@ static int rpmh_regulator_init_vreg(struct rpmh_vreg *vreg, struct device *dev,
> >       vreg->always_wait_for_ack = of_property_read_bool(node,
> >                                               "qcom,always-wait-for-ack");
> >
> > +     of_property_read_u32(node, "regulator-off-on-delay-us",
> > +                          &vreg->rdesc.off_on_delay);
>
> Would it not be a better fit for of_regulator.c?
>
> Konrad

Hi Konrad,

On Tue, Jan 27, 2026 at 4:00 PM Konrad Dybcio wrote:
> Would it not be a better fit for of_regulator.c?

That was my initial thought as well, but there is a limitation:

The `off_on_delay` field resides in `struct regulator_desc`. For most
regulator drivers, this structure is `static const` (immutable) as it describes
fixed silicon characteristics. Generic parsing code in `of_regulator.c`
cannot blindly write to `desc->off_on_delay` without risking a write to
read-only memory.

The `qcom-rpmh-regulator` driver is unique in that it allocates
`vreg->rdesc` dynamically at runtime, which allows us to safely populate
this field from DT.

To support this generically in `of_regulator.c`, we would likely need to
introduce `off_on_delay` into `struct regulator_constraints` instead,
and then update the core regulator handling to check both sources.

I opted for this driver-specific approach to minimize impact on the core
subsystem, given that `qcom-rpmh` is already set up to handle dynamic
descriptors.

Let me know if you would prefer I attempt the core framework change instead.

Regards,
Saikiran