[PATCH v3 0/3] Samsung Expressatt: Camera Flash

[PATCH v3 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 to the Samsung Expressatt's DTS

// Tests

// # Navigate to LED
sudo su
cd /sys/class/leds/white:flash

// # Should stay at dim brightness
echo 1 > brightness
echo 1 > brightness
echo 1 > brightness
echo 1 > brightness
echo 0 > brightness           # LED_OFF

// # Max Brightness
echo 50 > brightness
echo 0 > brightness           # LED_OFF
echo 99 > brightness
echo 0 > brightness           # LED_OFF
echo 1000 > brightness
echo 0 > brightness           # LED_OFF
echo 100 > brightness
echo 0 > brightness           # LED_OFF

// # Should increase in brightness
for i in $(seq 1 16); do echo $i > brightness; sleep 1; done
echo 0 > brightness           # LED_OFF

// # Test flash strobe (rt8515_led_flash_strobe_set)
cat max_flash_timeout          # check max
echo 200000 > flash_timeout    # 200ms
echo 1 > flash_strobe          # strobe ON → brightness_commit + timer
cat flash_strobe               # should read 1, then 0 after timeout
sleep 1
cat flash_strobe               # should be 0 (timer fired)

// # Test manual strobe cancel
echo 1 > flash_strobe ; echo 0 > flash_strobe          # immediate off

// # Check regulator error handling
dmesg | tail -20                     # look for any "failed to turn off LED" msgs

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 v3:
- DTS:
    - Renamed and reordered nodes
- Driver:
    - Use regulator_is_enabled() instead of reg_enabled
    - remove ent xor vin check
    - remove rt->reg == -ENODEV check
    - rename functions to reflect what they do and added ret's
    - Fixed: LED was increasing in brightness when setting the same
        brightness multiple times
- Link to v2: https://lore.kernel.org/r/20260318-expressatt_camera_flash-v2-0-5c2b9a623dcb@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                   | 90 +++++++++++++++++-----
 3 files changed, 148 insertions(+), 19 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 v3 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.

Assisted-by: Claude:claude-opus-4.6
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
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

[PATCH v3 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.

Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
---
 drivers/leds/flash/leds-rt8515.c | 90 ++++++++++++++++++++++++++++++++--------
 1 file changed, 72 insertions(+), 18 deletions(-)

diff --git a/drivers/leds/flash/leds-rt8515.c b/drivers/leds/flash/leds-rt8515.c
index f6b439674c03..739cac8789c8 100644
--- a/drivers/leds/flash/leds-rt8515.c
+++ b/drivers/leds/flash/leds-rt8515.c
@@ -63,16 +63,44 @@ static struct rt8515 *to_rt8515(struct led_classdev_flash *fled)
 	return container_of(fled, struct rt8515, fled);
 }
 
-static void rt8515_gpio_led_off(struct rt8515 *rt)
+static int rt8515_led_off(struct rt8515 *rt)
 {
+	int ret;
+
 	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);
+
+	/* Disable regulator */
+	ret = regulator_is_enabled(rt->reg);
+	if (ret < 0)
+		return ret;
+	if (ret > 0)
+		return regulator_disable(rt->reg);
+
+	return 0;
 }
 
-static void rt8515_gpio_brightness_commit(struct gpio_desc *gpiod,
-					  int brightness)
+static int rt8515_set_flash_brightness(struct rt8515 *rt,
+					 struct gpio_desc *gpiod,
+					 int brightness)
 {
 	int i;
+	int ret;
+
+	/*
+	 * Reset the IC to start brightness from zero,
+	 * then re-enable and pulse to the desired level.
+	 */
+	ret = rt8515_led_off(rt);
+	if (ret)
+		return ret;
+	/* IC needs time to reset its brightness counter */
+	usleep_range(100, 200);
+	/* Enable regulator */
+	ret = regulator_enable(rt->reg);
+	if (ret)
+		return ret;
 
 	/*
 	 * Toggling a GPIO line with a small delay increases the
@@ -84,31 +112,41 @@ static void rt8515_gpio_brightness_commit(struct gpio_desc *gpiod,
 		gpiod_set_value(gpiod, 1);
 		udelay(1);
 	}
+
+	return 0;
 }
 
 /* This is setting the torch light level */
-static int rt8515_led_brightness_set(struct led_classdev *led,
+static int rt8515_set_brightness(struct led_classdev *led,
 				     enum led_brightness brightness)
 {
 	struct led_classdev_flash *fled = lcdev_to_flcdev(led);
 	struct rt8515 *rt = to_rt8515(fled);
+	int ret = 0;
 
 	mutex_lock(&rt->lock);
 
 	if (brightness == LED_OFF) {
 		/* Off */
-		rt8515_gpio_led_off(rt);
+		ret = rt8515_led_off(rt);
+		if (ret)
+			goto out;
 	} 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);
+		/* Step it up to movie mode brightness */
+		ret = rt8515_set_flash_brightness(rt, rt->enable_torch ?
+				rt->enable_torch : rt->enable_flash, brightness);
+		if (ret)
+			goto out;
 	} else {
 		/* 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,
@@ -117,27 +155,33 @@ 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 LED flash mode and set brightness */
-		rt8515_gpio_brightness_commit(rt->enable_flash, brightness);
+		ret = rt8515_set_flash_brightness(rt, rt->enable_flash, brightness);
+		if (ret)
+			goto out;
 		/* Set timeout */
 		mod_timer(&rt->powerdown_timer,
 			  jiffies + usecs_to_jiffies(timeout->val));
 	} else {
 		timer_delete_sync(&rt->powerdown_timer);
 		/* Turn the LED off */
-		rt8515_gpio_led_off(rt);
+		ret = rt8515_led_off(rt);
+		if (ret)
+			goto out;
 	}
 
 	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,
@@ -166,9 +210,12 @@ static const struct led_flash_ops rt8515_flash_ops = {
 static void rt8515_powerdown_timer(struct timer_list *t)
 {
 	struct rt8515 *rt = timer_container_of(rt, t, powerdown_timer);
+	int ret;
 
 	/* Turn the LED off */
-	rt8515_gpio_led_off(rt);
+	ret = rt8515_led_off(rt);
+	if (ret)
+		dev_err(rt->dev, "failed to turn off LED (%d)\n", ret);
 }
 
 static void rt8515_init_flash_timeout(struct rt8515 *rt)
@@ -298,12 +345,18 @@ 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 */
+	rt->reg = devm_regulator_get(dev, "vin");
+	if (IS_ERR(rt->reg))
+		return dev_err_probe(dev, PTR_ERR(rt->reg),
+				     "failed to get vin supply\n");
+
 	child = device_get_next_child_node(dev, NULL);
 	if (!child) {
 		dev_err(dev,
@@ -333,8 +386,9 @@ static int rt8515_probe(struct platform_device *pdev)
 
 	fled->ops = &rt8515_flash_ops;
 
-	led->max_brightness = rt->torch_max_intensity;
-	led->brightness_set_blocking = rt8515_led_brightness_set;
+	led->max_brightness = rt->enable_torch ?
+		rt->torch_max_intensity : rt->flash_max_intensity;
+	led->brightness_set_blocking = rt8515_set_brightness;
 	led->flags |= LED_CORE_SUSPENDRESUME | LED_DEV_CAP_FLASH;
 
 	mutex_init(&rt->lock);

-- 
2.53.0

[PATCH v3 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

Assisted-by: Claude:claude-opus-4.6
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..35514fd53e3d 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;
 	};
 
+	vreg_flash: regulator-flash {
+		compatible = "regulator-fixed";
+		regulator-name = "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";
+	};
+
+	led-controller {
+		compatible = "richtek,rt8515";
+		enf-gpios = <&tlmm 3 GPIO_ACTIVE_HIGH>;
+		vin-supply = <&vreg_flash>;
+		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>;
@@ -172,6 +199,13 @@ touchscreen@4a {
 };
 
 &tlmm {
+	cam_flash_en: cam-flash-en-state {
+		pins = "gpio3";
+		function = "gpio";
+		drive-strength = <16>;
+		bias-pull-down;
+	};
+
 	spi1_default: spi1-default-state {
 		mosi-pins {
 			pins = "gpio6";
@@ -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 v3 3/3] ARM: dts: qcom: msm8960: expressatt: Add camera flash

[Konrad Dybcio]

On 3/26/26 8:57 AM, 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
> 
> Assisted-by: Claude:claude-opus-4.6
> Reviewed-by: David Heidelberg <david@ixit.cz>
> Signed-off-by: Rudraksha Gupta <guptarud@gmail.com>
> ---

IDK what to do with the AI thing, but for the change itself:

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>

Konrad

Re: [PATCH v3 2/3] leds: flash: rt8515: Support single-GPIO flash ICs with vin supply

[Linus Walleij]

Hi Rudraksha,

this is starting to look good, some remaining snags below:

On Thu, Mar 26, 2026 at 8:57 AM Rudraksha Gupta via B4 Relay
<devnull+guptarud.gmail.com@kernel.org> wrote:

> -static void rt8515_gpio_brightness_commit(struct gpio_desc *gpiod,
> -                                         int brightness)
> +static int rt8515_set_flash_brightness(struct rt8515 *rt,
> +                                        struct gpio_desc *gpiod,
> +                                        int brightness)

Do not change the name of the function, it's confusing.
This is also used for setting the brightness of the torch, and after
this change it looks like the function is just for the flash.

>         } 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);
> +               /* Step it up to movie mode brightness */
> +               ret = rt8515_set_flash_brightness(rt, rt->enable_torch ?
> +                               rt->enable_torch : rt->enable_flash, brightness);
> +               if (ret)
> +                       goto out;

Add a comment befor this that if we don't have a separate torch
enable pin connected, we use the flash pin also for the torch.

Yours,
Linus Walleij