[PATCH v2 0/2] regulator: rpi-panel-v2: Add required vcc-supply

[PATCH v2 0/2] regulator: rpi-panel-v2: Add required vcc-supply

[Shashank Maurya]

This series adds a required vcc-supply property to both the dt-binding
and the driver:

- Patch 1/2: dt-bindings - documents the vcc-supply property and
    marks it required in the schema.
  - Patch 2/2: driver - uses devm_regulator_get() to obtain and enable
    the vcc supply at the start of probe, before any I2C access.

---
Changes in v2:
  - Made vcc-supply required instead of optional (devm_regulator_get()
    instead of devm_regulator_get_optional()).
  - Added vcc-supply to the required list in the dt-binding schema.

Changes in v1:
  - Initial submission with optional vcc-supply support.

To: Liam Girdwood <lgirdwood@gmail.com>
To: Mark Brown <broonie@kernel.org>
To: Rob Herring <robh@kernel.org>
To: Krzysztof Kozlowski <krzk+dt@kernel.org>
To: Conor Dooley <conor+dt@kernel.org>
To: Florian Fainelli <florian.fainelli@broadcom.com>
To: Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>
To: Marek Vasut <marek.vasut+renesas@mailbox.org>
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-rpi-kernel@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org

---
Shashank Maurya (2):
      dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property
      regulator: rpi-panel-v2: Add required vcc-supply support

 .../raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml    |  5 +++++
 drivers/regulator/rpi-panel-v2-regulator.c                   | 12 ++++++++++++
 2 files changed, 17 insertions(+)
---
base-commit: bd2a0c2d8c49ffb7acfcb0c1177af355ea417caf
change-id: 20260907-rpi_reg-8c6885b35e5b

Best regards,
--  
Shashank Maurya <shashank.maurya@oss.qualcomm.com>

[PATCH v2 1/2] dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

[Shashank Maurya]

Add a vcc-supply property to the Raspberry Pi 7" touchscreen panel V2
regulator binding and mark it as required. The panel controller MCU
needs an external power rail to be supplied before any I2C communication
can take place.

Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
---
 .../regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml  | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
index 37b9ed371b67..a6195e53be16 100644
--- a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
+++ b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
@@ -35,6 +35,9 @@ properties:
     const: 3
     description: See ../../pwm/pwm.yaml for description of the cell formats.
 
+  vcc-supply:
+    description: Regulator supplying power to the panel controller.
+
 additionalProperties: false
 
 required:
@@ -43,6 +46,7 @@ required:
   - gpio-controller
   - "#gpio-cells"
   - "#pwm-cells"
+  - vcc-supply
 
 examples:
   - |
@@ -55,6 +59,7 @@ examples:
         gpio-controller;
         #gpio-cells = <2>;
         #pwm-cells = <3>;
+        vcc-supply = <&vcc_reg>;
       };
     };
 

-- 
2.34.1

Re: [PATCH v2 1/2] dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Critical] Making `vcc-supply` a strictly required property breaks existing in-tree device trees and ABI compatibility.
--

commit 1cfb28295a002af7450cc6c89daa817a9abfb4b0
Author: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

This commit introduces a vcc-supply property to the Raspberry Pi 7"
touchscreen panel V2 regulator binding. It specifies the regulator supplying
power to the panel controller and marks it as a required property.

> diff --git a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> index 37b9ed371b67d..a6195e53be16b 100644
> --- a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> +++ b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
[ ... ]
> @@ -43,6 +46,7 @@ required:
>    - gpio-controller
>    - "#gpio-cells"
>    - "#pwm-cells"
> +  - vcc-supply

[Severity: Critical]
Does making this property strictly required introduce regressions for
existing in-tree device trees?

Looking at the current tree,
arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk-rpi-display-2.dtsi
uses this binding but does not define vcc-supply:

arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk-rpi-display-2.dtsi:
	mcu: gpio@45 {
		compatible = "raspberrypi,touchscreen-panel-regulator-v2";
		reg = <0x45>;
		gpio-controller;
        ...
	};

Since vcc-supply is now unconditionally required, wouldn't builds
incorporating this device tree now fail dtbs_check validation? 

Could this be made optional to preserve ABI compatibility, or should the
existing device tree nodes be updated in the same patch series to prevent
breakages?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260907-rpi_reg-v2-0-0c59aa60d31f@oss.qualcomm.com?part=1

Re: [PATCH v2 1/2] dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

[Dave Stevenson]

Hi Shashank

(Apologies for the earlier HTML version of this - I thought I had my
mail client under control)

On Mon, 7 Sept 2026 at 06:48, Shashank Maurya
<shashank.maurya@oss.qualcomm.com> wrote:
>
> Add a vcc-supply property to the Raspberry Pi 7" touchscreen panel V2
> regulator binding and mark it as required. The panel controller MCU
> needs an external power rail to be supplied before any I2C communication
> can take place.
>
> Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
> ---
>  .../regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml  | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> index 37b9ed371b67..a6195e53be16 100644
> --- a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> +++ b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> @@ -35,6 +35,9 @@ properties:
>      const: 3
>      description: See ../../pwm/pwm.yaml for description of the cell formats.
>
> +  vcc-supply:
> +    description: Regulator supplying power to the panel controller.
> +
>  additionalProperties: false
>
>  required:
> @@ -43,6 +46,7 @@ required:
>    - gpio-controller
>    - "#gpio-cells"
>    - "#pwm-cells"
> +  - vcc-supply

Adding a new property as "required" breaks all existing users. Adding
it as optional would be reasonable.

  Dave

>
>  examples:
>    - |
> @@ -55,6 +59,7 @@ examples:
>          gpio-controller;
>          #gpio-cells = <2>;
>          #pwm-cells = <3>;
> +        vcc-supply = <&vcc_reg>;
>        };
>      };
>
>
> --
> 2.34.1
>
>

Re: [PATCH v2 1/2] dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

[Conor Dooley]

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On Mon, Sep 07, 2026 at 02:24:09PM +0100, Dave Stevenson wrote:
> Hi Shashank
> 
> (Apologies for the earlier HTML version of this - I thought I had my
> mail client under control)
> 
> On Mon, 7 Sept 2026 at 06:48, Shashank Maurya
> <shashank.maurya@oss.qualcomm.com> wrote:
> >
> > Add a vcc-supply property to the Raspberry Pi 7" touchscreen panel V2
> > regulator binding and mark it as required. The panel controller MCU
> > needs an external power rail to be supplied before any I2C communication
> > can take place.
> >
> > Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
> > ---
> >  .../regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml  | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > index 37b9ed371b67..a6195e53be16 100644
> > --- a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > +++ b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > @@ -35,6 +35,9 @@ properties:
> >      const: 3
> >      description: See ../../pwm/pwm.yaml for description of the cell formats.
> >
> > +  vcc-supply:
> > +    description: Regulator supplying power to the panel controller.
> > +
> >  additionalProperties: false
> >
> >  required:
> > @@ -43,6 +46,7 @@ required:
> >    - gpio-controller
> >    - "#gpio-cells"
> >    - "#pwm-cells"
> > +  - vcc-supply
> 
> Adding a new property as "required" breaks all existing users. Adding
> it as optional would be reasonable.

It can be made required here, but never in the driver. If it's actually
required that something turn this on before the device can be used,
making it required is probably correct.

> 
>   Dave
> 
> >
> >  examples:
> >    - |
> > @@ -55,6 +59,7 @@ examples:
> >          gpio-controller;
> >          #gpio-cells = <2>;
> >          #pwm-cells = <3>;
> > +        vcc-supply = <&vcc_reg>;
> >        };
> >      };
> >
> >
> > --
> > 2.34.1
> >
> >

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Re: [PATCH v2 1/2] dt-bindings: regulator: rpi-panel-v2: Add required vcc-supply property

[Shashank Maurya]

On Mon, Sep 07, 2026 at 06:10:36PM +0100, Conor Dooley wrote:
> On Mon, Sep 07, 2026 at 02:24:09PM +0100, Dave Stevenson wrote:
> > Hi Shashank
> > 
> > (Apologies for the earlier HTML version of this - I thought I had my
> > mail client under control)
> > 
> > On Mon, 7 Sept 2026 at 06:48, Shashank Maurya
> > <shashank.maurya@oss.qualcomm.com> wrote:
> > >
> > > Add a vcc-supply property to the Raspberry Pi 7" touchscreen panel V2
> > > regulator binding and mark it as required. The panel controller MCU
> > > needs an external power rail to be supplied before any I2C communication
> > > can take place.
> > >
> > > Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
> > > ---
> > >  .../regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml  | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > > index 37b9ed371b67..a6195e53be16 100644
> > > --- a/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > > +++ b/Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator-v2.yaml
> > > @@ -35,6 +35,9 @@ properties:
> > >      const: 3
> > >      description: See ../../pwm/pwm.yaml for description of the cell formats.
> > >
> > > +  vcc-supply:
> > > +    description: Regulator supplying power to the panel controller.
> > > +
> > >  additionalProperties: false
> > >
> > >  required:
> > > @@ -43,6 +46,7 @@ required:
> > >    - gpio-controller
> > >    - "#gpio-cells"
> > >    - "#pwm-cells"
> > > +  - vcc-supply
> > 
> > Adding a new property as "required" breaks all existing users. Adding
> > it as optional would be reasonable.
> 
> It can be made required here, but never in the driver. If it's actually
> required that something turn this on before the device can be used,
> making it required is probably correct.

Thanks Dave for clarification. I also see one existing consumer of this 
regulator driver: arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk-rpi-display-2.dtsi

So, adding required in bindings will fail for this user. 
Apologies, I didn't notice this earlier.

> 
> > 
> >   Dave
> > 
> > >
> > >  examples:
> > >    - |
> > > @@ -55,6 +59,7 @@ examples:
> > >          gpio-controller;
> > >          #gpio-cells = <2>;
> > >          #pwm-cells = <3>;
> > > +        vcc-supply = <&vcc_reg>;
> > >        };
> > >      };
> > >
> > >
> > > --
> > > 2.34.1
> > >
> > >

[PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Shashank Maurya]

The Raspberry Pi 7" touchscreen panel V2 MCU requires an external power
rail to be enabled before any I2C register access is attempted. Use
devm_regulator_get() to obtain the vcc supply and enable it at the
start of probe.

Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
---
 drivers/regulator/rpi-panel-v2-regulator.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/regulator/rpi-panel-v2-regulator.c b/drivers/regulator/rpi-panel-v2-regulator.c
index 30b78aa75ee3..e54d675962e7 100644
--- a/drivers/regulator/rpi-panel-v2-regulator.c
+++ b/drivers/regulator/rpi-panel-v2-regulator.c
@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/pwm.h>
 #include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
 
 /* I2C registers of the microcontroller. */
 #define REG_ID		0x01
@@ -66,10 +67,21 @@ static int rpi_panel_v2_i2c_probe(struct i2c_client *i2c)
 		.parent		= &i2c->dev,
 		.reg_set_base	= REG_POWERON,
 	};
+	struct regulator *vcc;
 	struct regmap *regmap;
 	struct pwm_chip *pc;
 	int ret;
 
+	vcc = devm_regulator_get(&i2c->dev, "vcc");
+	if (IS_ERR(vcc))
+		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
+				     "Failed to get vcc supply\n");
+
+	ret = regulator_enable(vcc);
+	if (ret)
+		return dev_err_probe(&i2c->dev, ret,
+				     "Failed to enable vcc supply\n");
+
 	pc = devm_pwmchip_alloc(&i2c->dev, 1, 0);
 	if (IS_ERR(pc))
 		return PTR_ERR(pc);

-- 
2.34.1

Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The 'vcc' regulator is enabled via regulator_enable() but never disabled on probe error paths or device unbind, leading to an unbalanced enable count and a kernel WARN_ON.
--

commit 8a9dbdb2e982cccc3d4ff2c75ec2e1c0cd6c0e7e
Author: Shashank Maurya <shashank.maurya@oss.qualcomm.com>

regulator: rpi-panel-v2: Add required vcc-supply support

This commit adds external power rail support to the Raspberry Pi 7"
touchscreen panel V2 MCU. It obtains the vcc supply and enables it at the
start of the probe function.

> diff --git a/drivers/regulator/rpi-panel-v2-regulator.c b/drivers/regulator/rpi-panel-v2-regulator.c
> index 30b78aa75ee38..e54d675962e71 100644
> --- a/drivers/regulator/rpi-panel-v2-regulator.c
> +++ b/drivers/regulator/rpi-panel-v2-regulator.c
[ ... ]
> @@ -66,10 +67,21 @@ static int rpi_panel_v2_i2c_probe(struct i2c_client *i2c)
>  		.parent		= &i2c->dev,
>  		.reg_set_base	= REG_POWERON,
>  	};
> +	struct regulator *vcc;
>  	struct regmap *regmap;
>  	struct pwm_chip *pc;
>  	int ret;
>  
> +	vcc = devm_regulator_get(&i2c->dev, "vcc");
> +	if (IS_ERR(vcc))
> +		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
> +				     "Failed to get vcc supply\n");
> +
> +	ret = regulator_enable(vcc);
> +	if (ret)
> +		return dev_err_probe(&i2c->dev, ret,
> +				     "Failed to enable vcc supply\n");
> +

[Severity: High]
Does this leave the regulator enabled indefinitely if probe later fails,
or upon device unbind? The regulator is enabled manually via
regulator_enable(), but it is never disabled in the subsequent error paths
or device unbind sequences. 

When the devres framework later releases the regulator during cleanup, it
will detect an unbalanced enable count and trigger a kernel WARN_ON in
_regulator_put(), leaving the physical regulator on.

Would it be better to use devm_regulator_get_enable() instead so that
the disablement is handled automatically?

>  	pc = devm_pwmchip_alloc(&i2c->dev, 1, 0);
>  	if (IS_ERR(pc))
>  		return PTR_ERR(pc);

[Severity: High]
If devm_pwmchip_alloc() fails here, does it leak the enabled regulator?
The function returns directly, bypassing any cleanup of the vcc supply
that was just successfully enabled.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260907-rpi_reg-v2-0-0c59aa60d31f@oss.qualcomm.com?part=2

Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Marek Vasut]

On 9/7/26 7:46 AM, Shashank Maurya wrote:
> The Raspberry Pi 7" touchscreen panel V2 MCU requires an external power
> rail to be enabled before any I2C register access is attempted. Use
> devm_regulator_get() to obtain the vcc supply and enable it at the
> start of probe.
Which power rail is this ?

Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Dave Stevenson]

Hi Shashank and Marek

On Mon, 7 Sept 2026 at 07:12, Marek Vasut <marek.vasut@mailbox.org> wrote:
>
> On 9/7/26 7:46 AM, Shashank Maurya wrote:
> > The Raspberry Pi 7" touchscreen panel V2 MCU requires an external power
> > rail to be enabled before any I2C register access is attempted. Use
> > devm_regulator_get() to obtain the vcc supply and enable it at the
> > start of probe.
> Which power rail is this ?

It'll be the 3.3V rail on the FFC which is used for the MCU, touch
controller, and LCD controller.
The separate 5V supply on the V2 panels is only used for the backlight.

  Dave

Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Conor Dooley]

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On Mon, Sep 07, 2026 at 11:16:08AM +0530, Shashank Maurya wrote:
> The Raspberry Pi 7" touchscreen panel V2 MCU requires an external power
> rail to be enabled before any I2C register access is attempted. Use
> devm_regulator_get() to obtain the vcc supply and enable it at the
> start of probe.
> 
> Signed-off-by: Shashank Maurya <shashank.maurya@oss.qualcomm.com>
> ---
>  drivers/regulator/rpi-panel-v2-regulator.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/regulator/rpi-panel-v2-regulator.c b/drivers/regulator/rpi-panel-v2-regulator.c
> index 30b78aa75ee3..e54d675962e7 100644
> --- a/drivers/regulator/rpi-panel-v2-regulator.c
> +++ b/drivers/regulator/rpi-panel-v2-regulator.c
> @@ -11,6 +11,7 @@
>  #include <linux/module.h>
>  #include <linux/pwm.h>
>  #include <linux/regmap.h>
> +#include <linux/regulator/consumer.h>
>  
>  /* I2C registers of the microcontroller. */
>  #define REG_ID		0x01
> @@ -66,10 +67,21 @@ static int rpi_panel_v2_i2c_probe(struct i2c_client *i2c)
>  		.parent		= &i2c->dev,
>  		.reg_set_base	= REG_POWERON,
>  	};
> +	struct regulator *vcc;
>  	struct regmap *regmap;
>  	struct pwm_chip *pc;
>  	int ret;
>  
> +	vcc = devm_regulator_get(&i2c->dev, "vcc");
> +	if (IS_ERR(vcc))
> +		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
> +				     "Failed to get vcc supply\n");
> +
> +	ret = regulator_enable(vcc);
> +	if (ret)
> +		return dev_err_probe(&i2c->dev, ret,
> +				     "Failed to enable vcc supply\n");

This needs to be optional, because without it you'll break existing
devicetrees. Unless you can explain how all existing users are
nonfunctional (e.g. nothing ever enabled the supply, which seems
doubtful given this surely worked when it was added) this must remain
optional.

> +
>  	pc = devm_pwmchip_alloc(&i2c->dev, 1, 0);
>  	if (IS_ERR(pc))
>  		return PTR_ERR(pc);
> 
> -- 
> 2.34.1
> 

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Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Mark Brown]

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On Mon, Sep 07, 2026 at 06:06:24PM +0100, Conor Dooley wrote:
> On Mon, Sep 07, 2026 at 11:16:08AM +0530, Shashank Maurya wrote:

> > +	vcc = devm_regulator_get(&i2c->dev, "vcc");
> > +	if (IS_ERR(vcc))
> > +		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
> > +				     "Failed to get vcc supply\n");

> This needs to be optional, because without it you'll break existing
> devicetrees. Unless you can explain how all existing users are
> nonfunctional (e.g. nothing ever enabled the supply, which seems
> doubtful given this surely worked when it was added) this must remain
> optional.

The core will stub in a dummy regulator for mandatory supplies that
don't have anything mapped by firmware, otherwise essentially all
regualtors would be optional and our error handling would be a disaster
zone.

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Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Conor Dooley]

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On Mon, Sep 07, 2026 at 06:09:57PM +0100, Mark Brown wrote:
> On Mon, Sep 07, 2026 at 06:06:24PM +0100, Conor Dooley wrote:
> > On Mon, Sep 07, 2026 at 11:16:08AM +0530, Shashank Maurya wrote:
> 
> > > +	vcc = devm_regulator_get(&i2c->dev, "vcc");
> > > +	if (IS_ERR(vcc))
> > > +		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
> > > +				     "Failed to get vcc supply\n");
> 
> > This needs to be optional, because without it you'll break existing
> > devicetrees. Unless you can explain how all existing users are
> > nonfunctional (e.g. nothing ever enabled the supply, which seems
> > doubtful given this surely worked when it was added) this must remain
> > optional.
> 
> The core will stub in a dummy regulator for mandatory supplies that
> don't have anything mapped by firmware, otherwise essentially all
> regualtors would be optional and our error handling would be a disaster
> zone.

I always forget how this works. Thanks for the reminder.



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Re: [PATCH v2 2/2] regulator: rpi-panel-v2: Add required vcc-supply support

[Shashank Maurya]

On Mon, Sep 07, 2026 at 07:04:21PM +0100, Conor Dooley wrote:
> On Mon, Sep 07, 2026 at 06:09:57PM +0100, Mark Brown wrote:
> > On Mon, Sep 07, 2026 at 06:06:24PM +0100, Conor Dooley wrote:
> > > On Mon, Sep 07, 2026 at 11:16:08AM +0530, Shashank Maurya wrote:
> > 
> > > > +	vcc = devm_regulator_get(&i2c->dev, "vcc");
> > > > +	if (IS_ERR(vcc))
> > > > +		return dev_err_probe(&i2c->dev, PTR_ERR(vcc),
> > > > +				     "Failed to get vcc supply\n");
> > 
> > > This needs to be optional, because without it you'll break existing
> > > devicetrees. Unless you can explain how all existing users are
> > > nonfunctional (e.g. nothing ever enabled the supply, which seems
> > > doubtful given this surely worked when it was added) this must remain
> > > optional.
> > 
> > The core will stub in a dummy regulator for mandatory supplies that
> > don't have anything mapped by firmware, otherwise essentially all
> > regualtors would be optional and our error handling would be a disaster
> > zone.
> 
> I always forget how this works. Thanks for the reminder.
> 
> 

Thanks Mark and Conor for the clarification.

To summarize: the binding marks vcc-supply as required 
(since the hardware genuinely needs this rail), and the driver uses 
devm_regulator_get() which lets the regulator core provide a dummy 
stub for existing devicetrees that don't specify the supply. 
This keeps backward compatibility intact.

Is the series good to go as-is, or is there anything else you'd like 
me to address in a v3?