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

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Message-ID: <99aa1a81-e64d-4ea8-b69d-3ce08b9994a3@oss.qualcomm.com>
Date: Wed, 28 Jan 2026 12:42:12 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Saikiran B <bjsaikiran@...il.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 1/28/26 12:34 PM, Saikiran B wrote:
> 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.

I'm a fly-by reviewer for this sort of thing (as you can see by me not
knowing this reasoning..)

Mark (the maintainer) should be able to give you a more insightful answer

Konrad