Re: [PATCH v3 0/2] regulator: qcom-rpmh: Add off-on-delay support

[Kamal Wadhwa]

On Wed, Jan 28, 2026 at 12:32:09AM +0530, Saikiran wrote:
> This series adds support for the standard `regulator-off-on-delay-us`
> property to the Qualcomm RPMh regulator driver and updates the
> corresponding Device Tree bindings.
> 
> Motivation:
> On the Lenovo Yoga Slim 7x (Snapdragon X Elite), the camera regulators
> (LDO1, LDO3, LDO7) have large bulk capacitors and rely on passive discharge.
> When these regulators are disabled, the voltage decays very slowly. If
> re-enabled too quickly, the sensor experiences a brownout and fails to
> initialize.
> 
> Verification:
> I verified that the core `drivers/regulator/of_regulator.c` does not
> currently parse `regulator-off-on-delay-us` in `of_get_regulation_constraints()`.
> Therefore, the driver must parse this property explicitly and populate
> `rdesc->off_on_delay` so the regulator core can enforce the constraint.
> 
> Changes in v3:
> - Added Patch 1/2: Update DT bindings to allow `regulator-off-on-delay-us`
>   for `qcom,rpmh-regulator` (Requested by Mark Brown).
> - Updated Patch 2/2: Refined commit message to explicitly mention the
>   passive discharge and bulk capacitor mechanism on the Yoga Slim 7x
>   (Requested by Mark Brown).
> 
> Changes in v2:
> - Moved the motivation/context from the cover letter into the commit
>   message of the driver patch.
> 
> Saikiran (2):
>   dt-bindings: regulator: qcom,rpmh: Allow regulator-off-on-delay-us
>   regulator: qcom-rpmh: Add support for regulator-off-on-delay-us

Hi Mark, Bjorn, Konrad and all,

We have another UFS issue on QCS8300 RB4 EVK, where it seems this patch is
helping.

Issue is seen 2/10 reboots and it happens in the UFS probe defer path:

1. UFS probe takes regulator handle for VCC(vreg_l8a) of UFS host controller.
2. UFS probe enables the regulator
3. UFS probe defers (due to some other dependency un-related to regulator)
4. UFS regulator disabled on probe exit
5. UFS re-attempts probe and re-enables the regulator
6. UFS init sequence runs -> UFS NOP OUT command failed (no shell) 

Issue Log:

[    6.583836] ufshcd-qcom 1d84000.ufs: ufshcd_verify_dev_init: NOP OUT failed -11
[    6.592780] ufshcd-qcom 1d84000.ufs: ufshcd_async_scan failed: -11

NOTE
- Issue is not seen in first probe attempt, because UFS regulators are left ON
  from bootloader, which gives enough time between rail turn ON and UFS init
  sequence start.  However in issue case, it seems re-probe is happening too
  fast, which causes init sequence to fail and UFS brownouts (similar to camera
  sensor case)

- Also, we compared this board with other RBxx EVK boards for UFS rail, it
  seems that this board has more caps on the VCC regulator, as the board is
  designed to have both EMMC and UFS, and we have DT option to pick one of them.

  So for EMMC those extra caps were added and they are impacting rampup on VCC.

Since this is not entirely a UFS part issue, but a board design constraint, it
seems better if we handle this in the regulator side itself, as adding it in the
UFS driver may not be acceptable from UFS reviewers.

Please share your opinion, if this seems to be good reason to accept this patch?

Regards,
Kamal