[PATCH v2 0/3] Samsung Expressatt: Camera Flash

[PATCH v2 0/3] Samsung Expressatt: Camera Flash

[Rudraksha Gupta via B4 Relay]

This small series adds camera flash to an existing similar mainline
driver and adds it the the Samsung Expressatt's DTS

Assisted by AI (Claude).

Downstream reference:
Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/drivers/leds/Makefile#L51
Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/arch/arm/mach-msm/board-apexq-camera.c#L591

Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
---
Changes in v2:
- dt-bindings: Explain the hardware and not the driver
- **/*: Use vin-supply instead of unlock-gpio
- expressatt DTS: Reorder pinctrl-*
- expressatt DTS: Define rfs-ohms to a default (couldn't find
                  information about this)
- Link to v1: https://lore.kernel.org/r/20260306-expressatt_camera_flash-v1-0-b1996f7cdfdd@gmail.com

---
Rudraksha Gupta (3):
      dt-bindings: leds: rt8515: Support single-GPIO flash ICs with vin supply
      leds: flash: rt8515: Support single-GPIO flash ICs with vin supply
      ARM: dts: qcom: msm8960: expressatt: Add camera flash

 .../devicetree/bindings/leds/richtek,rt8515.yaml   | 34 +++++++++++-
 .../dts/qcom/qcom-msm8960-samsung-expressatt.dts   | 43 +++++++++++++++
 drivers/leds/flash/leds-rt8515.c                   | 64 +++++++++++++++++++---
 3 files changed, 132 insertions(+), 9 deletions(-)
---
base-commit: e9ec05addd1a067fc7cb218f20ecdc1b1b0898c0
change-id: 20260306-expressatt_camera_flash-13c15a7427aa
prerequisite-message-id: <20251205-expressatt-touchkey-v1-1-1444b927c9f3@gmail.com>
prerequisite-patch-id: 8de4de7909722ccaf385c4224f25a623eaa72c28

Best regards,
-- 
Rudraksha Gupta <guptarud@gmail.com>

[PATCH v2 1/3] dt-bindings: leds: rt8515: Support single-GPIO flash ICs with vin supply

[Rudraksha Gupta via B4 Relay]

From: Rudraksha Gupta <guptarud@gmail.com>

Some flash ICs use the same one-wire pulse-count protocol as the RT8515
but have only a single enable line for both flash and torch modes, plus
an optional input voltage supply (e.g. a GPIO-controlled fixed
regulator) that gates power to the chip.

Make ent-gpios optional and add a vin-supply property to support these
variants. Add a oneOf constraint requiring exactly one of ent-gpios or
vin-supply. Add a binding example showing the single-GPIO configuration
with an input supply.

Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
---
 .../devicetree/bindings/leds/richtek,rt8515.yaml   | 34 +++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/leds/richtek,rt8515.yaml b/Documentation/devicetree/bindings/leds/richtek,rt8515.yaml
index 0356371a6b01..ab3c5139132c 100644
--- a/Documentation/devicetree/bindings/leds/richtek,rt8515.yaml
+++ b/Documentation/devicetree/bindings/leds/richtek,rt8515.yaml
@@ -15,6 +15,10 @@ description: |
   current for each mode is defined in hardware using two resistors
   RFS and RTS.
 
+  Some flash ICs use the same one-wire pulse-count protocol but have
+  only a single enable line for both flash and torch modes. For these
+  single-channel variants, only enf-gpios is needed.
+
 properties:
   compatible:
     const: richtek,rt8515
@@ -26,6 +30,11 @@ properties:
   ent-gpios:
     maxItems: 1
     description: A connection to the 'ENT' (enable torch) pin.
+      Not present on single-channel flash ICs that use only one enable
+      line for both flash and torch modes.
+
+  vin-supply:
+    description: Optional input supply for the flash IC.
 
   richtek,rfs-ohms:
     minimum: 7680
@@ -81,10 +90,15 @@ properties:
 
 required:
   - compatible
-  - ent-gpios
   - enf-gpios
   - led
 
+oneOf:
+  - required:
+      - ent-gpios
+  - required:
+      - vin-supply
+
 additionalProperties: false
 
 examples:
@@ -108,4 +122,22 @@ examples:
         };
     };
 
+  - |
+    /* Single-channel flash IC with input supply */
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/leds/common.h>
+
+    led-controller {
+        compatible = "richtek,rt8515";
+        enf-gpios = <&tlmm 3 GPIO_ACTIVE_HIGH>;
+        vin-supply = <&flash_reg>;
+        richtek,rfs-ohms = <16000>;
+
+        led {
+            function = LED_FUNCTION_FLASH;
+            color = <LED_COLOR_ID_WHITE>;
+            flash-max-timeout-us = <250000>;
+        };
+    };
+
 ...

-- 
2.53.0

Re: [PATCH v2 1/3] dt-bindings: leds: rt8515: Support single-GPIO flash ICs with vin supply

[Linus Walleij]

On Wed, Mar 18, 2026 at 7:34 PM Rudraksha Gupta via B4 Relay
<devnull+guptarud.gmail.com@kernel.org> wrote:

> From: Rudraksha Gupta <guptarud@gmail.com>
>
> Some flash ICs use the same one-wire pulse-count protocol as the RT8515
> but have only a single enable line for both flash and torch modes, plus
> an optional input voltage supply (e.g. a GPIO-controlled fixed
> regulator) that gates power to the chip.
>
> Make ent-gpios optional and add a vin-supply property to support these
> variants. Add a oneOf constraint requiring exactly one of ent-gpios or
> vin-supply. Add a binding example showing the single-GPIO configuration
> with an input supply.
>
> Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>

This looks right to me!
Reviewed-by: Linus Walleij <linusw@kernel.org>

Yours,
Linus Walleij

Re: [PATCH v2 1/3] dt-bindings: leds: rt8515: Support single-GPIO flash ICs with vin supply

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 75 bytes --]

Acked-by: Conor Dooley <conor.dooley@microchip.com>
pw-bot: not-applicable

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

[PATCH v2 2/3] leds: flash: rt8515: Support single-GPIO flash ICs with vin supply

[Rudraksha Gupta via B4 Relay]

From: Rudraksha Gupta <guptarud@gmail.com>

Extend the RT8515 driver to support flash ICs that use only a single
GPIO for both flash and torch modes (no separate ENT pin), with an
optional vin regulator that gates power to the flash IC.

When vin-supply is provided, the driver enables the regulator before
activating the LED and disables it when turning off.

Make ent-gpios optional and validate at probe time that exactly one of
ent-gpios or vin-supply is provided. When ent-gpios is absent, the
driver uses enf-gpios for both flash and torch brightness control.

Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
---
 drivers/leds/flash/leds-rt8515.c | 64 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 56 insertions(+), 8 deletions(-)

diff --git a/drivers/leds/flash/leds-rt8515.c b/drivers/leds/flash/leds-rt8515.c
index f6b439674c03..69cfd5cba921 100644
--- a/drivers/leds/flash/leds-rt8515.c
+++ b/drivers/leds/flash/leds-rt8515.c
@@ -50,6 +50,7 @@ struct rt8515 {
 	struct v4l2_flash *v4l2_flash;
 	struct mutex lock;
 	struct regulator *reg;
+	bool reg_enabled;
 	struct gpio_desc *enable_torch;
 	struct gpio_desc *enable_flash;
 	struct timer_list powerdown_timer;
@@ -66,7 +67,12 @@ static struct rt8515 *to_rt8515(struct led_classdev_flash *fled)
 static void rt8515_gpio_led_off(struct rt8515 *rt)
 {
 	gpiod_set_value(rt->enable_flash, 0);
-	gpiod_set_value(rt->enable_torch, 0);
+	if (rt->enable_torch)
+		gpiod_set_value(rt->enable_torch, 0);
+	if (rt->reg && rt->reg_enabled) {
+		regulator_disable(rt->reg);
+		rt->reg_enabled = false;
+	}
 }
 
 static void rt8515_gpio_brightness_commit(struct gpio_desc *gpiod,
@@ -92,6 +98,7 @@ static int rt8515_led_brightness_set(struct led_classdev *led,
 {
 	struct led_classdev_flash *fled = lcdev_to_flcdev(led);
 	struct rt8515 *rt = to_rt8515(fled);
+	int ret = 0;
 
 	mutex_lock(&rt->lock);
 
@@ -99,16 +106,33 @@ static int rt8515_led_brightness_set(struct led_classdev *led,
 		/* Off */
 		rt8515_gpio_led_off(rt);
 	} else if (brightness < RT8515_TORCH_MAX) {
-		/* Step it up to movie mode brightness using the flash pin */
-		rt8515_gpio_brightness_commit(rt->enable_torch, brightness);
+		/* Enable the vin regulator if needed */
+		if (rt->reg && !rt->reg_enabled) {
+			ret = regulator_enable(rt->reg);
+			if (ret)
+				goto out;
+			rt->reg_enabled = true;
+		}
+		/* Step it up to movie mode brightness */
+		rt8515_gpio_brightness_commit(rt->enable_torch ?
+				rt->enable_torch : rt->enable_flash, brightness);
 	} else {
+		/* Enable the vin regulator if needed */
+		if (rt->reg && !rt->reg_enabled) {
+			ret = regulator_enable(rt->reg);
+			if (ret)
+				goto out;
+			rt->reg_enabled = true;
+		}
 		/* Max torch brightness requested */
-		gpiod_set_value(rt->enable_torch, 1);
+		gpiod_set_value(rt->enable_torch ? rt->enable_torch :
+				rt->enable_flash, 1);
 	}
 
+out:
 	mutex_unlock(&rt->lock);
 
-	return 0;
+	return ret;
 }
 
 static int rt8515_led_flash_strobe_set(struct led_classdev_flash *fled,
@@ -117,10 +141,18 @@ static int rt8515_led_flash_strobe_set(struct led_classdev_flash *fled,
 	struct rt8515 *rt = to_rt8515(fled);
 	struct led_flash_setting *timeout = &fled->timeout;
 	int brightness = rt->flash_max_intensity;
+	int ret = 0;
 
 	mutex_lock(&rt->lock);
 
 	if (state) {
+		/* Enable the vin regulator if needed */
+		if (rt->reg && !rt->reg_enabled) {
+			ret = regulator_enable(rt->reg);
+			if (ret)
+				goto out;
+			rt->reg_enabled = true;
+		}
 		/* Enable LED flash mode and set brightness */
 		rt8515_gpio_brightness_commit(rt->enable_flash, brightness);
 		/* Set timeout */
@@ -135,9 +167,10 @@ static int rt8515_led_flash_strobe_set(struct led_classdev_flash *fled,
 	fled->led_cdev.brightness = LED_OFF;
 	/* After this the torch LED will be disabled */
 
+out:
 	mutex_unlock(&rt->lock);
 
-	return 0;
+	return ret;
 }
 
 static int rt8515_led_flash_strobe_get(struct led_classdev_flash *fled,
@@ -298,12 +331,27 @@ static int rt8515_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(rt->enable_flash),
 				     "cannot get ENF (enable flash) GPIO\n");
 
-	/* ENT - Enable Torch line */
-	rt->enable_torch = devm_gpiod_get(dev, "ent", GPIOD_OUT_LOW);
+	/* ENT - Enable Torch line (optional for single-GPIO flash ICs) */
+	rt->enable_torch = devm_gpiod_get_optional(dev, "ent", GPIOD_OUT_LOW);
 	if (IS_ERR(rt->enable_torch))
 		return dev_err_probe(dev, PTR_ERR(rt->enable_torch),
 				     "cannot get ENT (enable torch) GPIO\n");
 
+	/* Optional VIN supply (e.g. GPIO-controlled fixed regulator) */
+	rt->reg = devm_regulator_get_optional(dev, "vin");
+	if (IS_ERR(rt->reg)) {
+		if (PTR_ERR(rt->reg) == -ENODEV)
+			rt->reg = NULL;
+		else
+			return dev_err_probe(dev, PTR_ERR(rt->reg),
+					     "failed to get vin supply\n");
+	}
+
+	/* Exactly one of ENT or VIN must be provided */
+	if (!rt->enable_torch == !rt->reg)
+		return dev_err_probe(dev, -EINVAL,
+				     "exactly one of ent-gpios or vin-supply is required\n");
+
 	child = device_get_next_child_node(dev, NULL);
 	if (!child) {
 		dev_err(dev,

-- 
2.53.0

Re: [PATCH v2 2/3] leds: flash: rt8515: Support single-GPIO flash ICs with vin supply

[Linus Walleij]

Hi Rudraksha,

this is a clear improvement! I like the directions this
is going.

Mark Brown needs to look at how you're using regulators
here.

On Wed, Mar 18, 2026 at 7:34 PM Rudraksha Gupta via B4 Relay
<devnull+guptarud.gmail.com@kernel.org> wrote:

> From: Rudraksha Gupta <guptarud@gmail.com>
>
> Extend the RT8515 driver to support flash ICs that use only a single
> GPIO for both flash and torch modes (no separate ENT pin), with an
> optional vin regulator that gates power to the flash IC.
>
> When vin-supply is provided, the driver enables the regulator before
> activating the LED and disables it when turning off.
>
> Make ent-gpios optional and validate at probe time that exactly one of
> ent-gpios or vin-supply is provided. When ent-gpios is absent, the
> driver uses enf-gpios for both flash and torch brightness control.
>
> Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>

(...)

>         struct regulator *reg;
> +       bool reg_enabled;

I think you can actually ask a regulator if it is enabled already,
regulator_is_enabled().

Also as long as you enable and disable it the same number of
times it also contains an internal reference count, so this is
often enough.

> +       if (rt->reg && rt->reg_enabled) {
> +               regulator_disable(rt->reg);
> +               rt->reg_enabled = false;
> +       }

I don't think you need to NULL-check rt-reg but not sure.

Can you use regulator_is_enabled() instead of the bool local?

> +               /* Enable the vin regulator if needed */
> +               if (rt->reg && !rt->reg_enabled) {

Dito

> +               /* Enable the vin regulator if needed */
> +               if (rt->reg && !rt->reg_enabled) {
> +                       ret = regulator_enable(rt->reg);

Dito

>         if (state) {
> +               /* Enable the vin regulator if needed */
> +               if (rt->reg && !rt->reg_enabled) {

Dito.

> +       /* Optional VIN supply (e.g. GPIO-controlled fixed regulator) */
> +       rt->reg = devm_regulator_get_optional(dev, "vin");
> +       if (IS_ERR(rt->reg)) {
> +               if (PTR_ERR(rt->reg) == -ENODEV)
> +                       rt->reg = NULL;

I think the regulator callbacks are able to deal transparently
with "regulators" that are -ENODEV, can you just let it pass?
Anyway Mark knows what to do here.

> +       /* Exactly one of ENT or VIN must be provided */
> +       if (!rt->enable_torch == !rt->reg)
> +               return dev_err_probe(dev, -EINVAL,
> +                                    "exactly one of ent-gpios or vin-supply is required\n");

Please drop this check.

I think there can be systems using the torch but also define
the regulator.

Yours,
Linus Walleij

[PATCH v2 3/3] ARM: dts: qcom: msm8960: expressatt: Add camera flash

[Rudraksha Gupta via B4 Relay]

From: Rudraksha Gupta <guptarud@gmail.com>

Add camera flash support for the Samsung Galaxy Express (expressatt).

The flash IC uses a one-wire pulse-count protocol on GPIO 3, powered
by a GPIO-controlled fixed regulator on PMIC MPP 4. The regulator is
modeled as a regulator-fixed node and supplied to the flash IC via
vin-supply.

Downstream references:
Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/drivers/leds/Makefile#L51
Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/arch/arm/mach-msm/board-apexq-camera.c#L591

Reviewed-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
---
 .../dts/qcom/qcom-msm8960-samsung-expressatt.dts   | 43 ++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts b/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
index c4b98af6955d..ad5169a60937 100644
--- a/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
+++ b/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <dt-bindings/input/input.h>
+#include <dt-bindings/leds/common.h>
 #include <dt-bindings/reset/qcom,gcc-msm8960.h>
 
 #include "qcom-msm8960.dtsi"
@@ -61,6 +62,32 @@ touchkey_enable: touchkey-enable {
 		regulator-boot-on;
 	};
 
+	flash_gpio_reg: regulator-flash {
+		compatible = "regulator-fixed";
+		regulator-name = "flash_led_en";
+		regulator-min-microvolt = <3300000>;
+		regulator-max-microvolt = <3300000>;
+		gpio = <&pm8921_mpps 4 GPIO_ACTIVE_HIGH>;
+		enable-active-high;
+		pinctrl-0 = <&flash_led_unlock>;
+		pinctrl-names = "default";
+	};
+
+	camera_flash: led-controller {
+		compatible = "richtek,rt8515";
+		enf-gpios = <&tlmm 3 GPIO_ACTIVE_HIGH>;
+		vin-supply = <&flash_gpio_reg>;
+		richtek,rfs-ohms = <16000>;
+		pinctrl-0 = <&cam_flash_en>;
+		pinctrl-names = "default";
+
+		led {
+			function = LED_FUNCTION_FLASH;
+			color = <LED_COLOR_ID_WHITE>;
+			flash-max-timeout-us = <250000>;
+		};
+	};
+
 	i2c-gpio-touchkey {
 		compatible = "i2c-gpio";
 		#address-cells = <1>;
@@ -247,6 +274,13 @@ touchkey_irq_pin: touchkey-irq-state {
 		drive-strength = <2>;
 		bias-disable;
 	};
+
+	cam_flash_en: cam-flash-en-state {
+		pins = "gpio3";
+		function = "gpio";
+		drive-strength = <16>;
+		bias-pull-down;
+	};
 };
 
 &pm8921 {
@@ -572,3 +606,12 @@ magnetometer@2e {
 		/* TODO: Figure out Mount Matrix */
 	};
 };
+
+&pm8921_mpps {
+	flash_led_unlock: flash-led-unlock-state {
+		pins = "mpp4";
+		function = "digital";
+		output-low;
+		power-source = <PM8921_GPIO_S4>;
+	};
+};

-- 
2.53.0

Re: [PATCH v2 3/3] ARM: dts: qcom: msm8960: expressatt: Add camera flash

[Konrad Dybcio]

On 3/18/26 7:34 PM, Rudraksha Gupta via B4 Relay wrote:
> From: Rudraksha Gupta <guptarud@gmail.com>
> 
> Add camera flash support for the Samsung Galaxy Express (expressatt).
> 
> The flash IC uses a one-wire pulse-count protocol on GPIO 3, powered
> by a GPIO-controlled fixed regulator on PMIC MPP 4. The regulator is
> modeled as a regulator-fixed node and supplied to the flash IC via
> vin-supply.
> 
> Downstream references:
> Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/drivers/leds/Makefile#L51
> Link: https://github.com/LineageOS/android_kernel_samsung_d2/blob/stable/cm-12.0-YNG4N/arch/arm/mach-msm/board-apexq-camera.c#L591
> 
> Reviewed-by: David Heidelberg <david@ixit.cz>
> Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
> ---
>  .../dts/qcom/qcom-msm8960-samsung-expressatt.dts   | 43 ++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts b/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
> index c4b98af6955d..ad5169a60937 100644
> --- a/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
> +++ b/arch/arm/boot/dts/qcom/qcom-msm8960-samsung-expressatt.dts
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <dt-bindings/input/input.h>
> +#include <dt-bindings/leds/common.h>
>  #include <dt-bindings/reset/qcom,gcc-msm8960.h>
>  
>  #include "qcom-msm8960.dtsi"
> @@ -61,6 +62,32 @@ touchkey_enable: touchkey-enable {
>  		regulator-boot-on;
>  	};
>  
> +	flash_gpio_reg: regulator-flash {

"vreg_flash:"

> +		compatible = "regulator-fixed";
> +		regulator-name = "flash_led_en";

"_en" makes it sound like it's an enable pin - if we don't have a better
idea, perhaps VREG_FLASH_3P3?

> +		regulator-min-microvolt = <3300000>;
> +		regulator-max-microvolt = <3300000>;
> +		gpio = <&pm8921_mpps 4 GPIO_ACTIVE_HIGH>;
> +		enable-active-high;
> +		pinctrl-0 = <&flash_led_unlock>;
> +		pinctrl-names = "default";
> +	};
> +
> +	camera_flash: led-controller {

Let's drop the label since it's unused

> +		compatible = "richtek,rt8515";
> +		enf-gpios = <&tlmm 3 GPIO_ACTIVE_HIGH>;
> +		vin-supply = <&flash_gpio_reg>;
> +		richtek,rfs-ohms = <16000>;
> +		pinctrl-0 = <&cam_flash_en>;
> +		pinctrl-names = "default";
> +
> +		led {
> +			function = LED_FUNCTION_FLASH;
> +			color = <LED_COLOR_ID_WHITE>;
> +			flash-max-timeout-us = <250000>;
> +		};
> +	};
> +
>  	i2c-gpio-touchkey {
>  		compatible = "i2c-gpio";
>  		#address-cells = <1>;
> @@ -247,6 +274,13 @@ touchkey_irq_pin: touchkey-irq-state {

This label from the context seems not to be present in -next, FWIW

>  		drive-strength = <2>;
>  		bias-disable;
>  	};
> +
> +	cam_flash_en: cam-flash-en-state {
> +		pins = "gpio3";

Please keep the pinctrl entries sorted by the GPIO index

Konrad