linux-kernel - Re: [PATCH v1 2/2] PCI: j721e: Add support for optional regulator supplies

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Message-ID: <91e8f4346a677a2ea46a210d7422adb99e70b3be.camel@gmail.com>
Date: Mon, 27 Oct 2025 20:24:12 +0000
From: Vitor Soares <ivitro@...il.com>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Vignesh Raghavendra <vigneshr@...com>, Siddharth Vadapalli
	 <s-vadapalli@...com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof
	Wilczyński
	 <kwilczynski@...nel.org>, Rob Herring <robh@...nel.org>, Bjorn Helgaas
	 <bhelgaas@...gle.com>, Vitor Soares <vitor.soares@...adex.com>, 
	linux-omap@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] PCI: j721e: Add support for optional regulator
 supplies

Hello Mani,

Thank you for the feedback.

On Tue, 2025-10-21 at 07:36 +0530, Manivannan Sadhasivam wrote:
> On Tue, Oct 14, 2025 at 12:25:49PM +0100, Vitor Soares wrote:
> > From: Vitor Soares <vitor.soares@...adex.com>
> > 
> > Some boards require external regulators to power PCIe endpoints.
> > Add support for optional 1.5V, 3.3V, and 12V supplies, which may be
> > defined in the device tree as vpcie1v5-supply, vpcie3v3-supply, and
> > vpcie12v-supply.
> > 
> > Use devm_regulator_get_enable_optional() to obtain and enable each
> > supply, so it will be automatically disabled when the driver is
> > removed.
> > 
> > Signed-off-by: Vitor Soares <vitor.soares@...adex.com>
> > ---
> >  drivers/pci/controller/cadence/pci-j721e.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/cadence/pci-j721e.c
> > b/drivers/pci/controller/cadence/pci-j721e.c
> > index 5bc5ab20aa6d..f29ce2aef04e 100644
> > --- a/drivers/pci/controller/cadence/pci-j721e.c
> > +++ b/drivers/pci/controller/cadence/pci-j721e.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/platform_device.h>
> >  #include <linux/pm_runtime.h>
> >  #include <linux/regmap.h>
> > +#include <linux/regulator/consumer.h>
> >  
> >  #include "../../pci.h"
> >  #include "pcie-cadence.h"
> > @@ -467,6 +468,10 @@ static const struct of_device_id of_j721e_pcie_match[]
> > = {
> >  };
> >  MODULE_DEVICE_TABLE(of, of_j721e_pcie_match);
> >  
> > +static const char * const j721e_pcie_supplies[] = {
> > +       "vpcie12v", "vpcie3v3", "vpcie1v5"
> > +};
> 
> Please don't hardcode the supplies in driver. The DT binding should make sure
> the relevant supplies are passed (including the optional ones). Just use
> of_regulator_bulk_get_all() to acquire all the passed supplies.
> 
> - Mani
> 

I checked the bulk regulator APIs as suggested and of_regulator_bulk_get_all()
does handle optional supplies correctly, however it is not a managed function
and doesn't enable the  regulators automatically.

To use of_regulator_bulk_get_all(), I would need to:
- Manually enable regulators with regulator_bulk_enable()
- Add cleanup/disable logic in remove path
- Handle error cleanup path manually

This would actually make the code more complex and error-prone compared to the
current approach using devm_regulator_get_enable_optional(), which provides
managed cleanup and automatic enable for optional supplies.

I also checked devm_regulator_bulk_get_enable(), it treats all supplies as
required and needs the supplies name as well.

Unless there is a devm_regulator_bulk_get_optional_enable() API I'm not aware
of, the current per-supply approach is the standard kernel pattern for this use
case. Would you still prefer the bulk approach despite these limitations?

Best regards,
Vitor Soares