[PATCH v2 0/2] Kinetic KTD2801 backlight driver

[PATCH v2 0/2] Kinetic KTD2801 backlight driver

[Duje Mihanović]

Hello,

This small series adds a driver for the Kinetic KTD2801 backlight IC.
The driver has been tested on the samsung,coreprimevelte for which
support is still out-of-tree.

Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
---
Changes in v2:
- Address maintainer comments:
  - Drop MODULE_ALIAS
  - Rename enable-gpios to ctrl-gpios
  - Rename ktd2801_backlight->desc to ktd2801_backlight->gpiod
  - Give time constants more descriptive names and note their origins in
    Samsung driver
  - Convert to GPIO_ACTIVE_HIGH
- Update trailers
- Link to v1: https://lore.kernel.org/r/20231005-ktd2801-v1-0-43cd85b0629a@skole.hr

---
Duje Mihanović (2):
      dt-bindings: backlight: add Kinetic KTD2801 binding
      backlight: Add Kinetic KTD2801 driver

 .../bindings/leds/backlight/kinetic,ktd2801.yaml   |  46 +++++++
 MAINTAINERS                                        |   6 +
 drivers/video/backlight/Kconfig                    |   7 +
 drivers/video/backlight/Makefile                   |   1 +
 drivers/video/backlight/ktd2801-backlight.c        | 149 +++++++++++++++++++++
 5 files changed, 209 insertions(+)
---
base-commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a
change-id: 20231004-ktd2801-0f3883cb59d0

Best regards,
-- 
Duje Mihanović <duje.mihanovic@skole.hr>

[PATCH v2 1/2] dt-bindings: backlight: add Kinetic KTD2801 binding

[Duje Mihanović]

Add the dt binding for the Kinetic KTD2801 backlight driver.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
---
 .../bindings/leds/backlight/kinetic,ktd2801.yaml   | 46 ++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/kinetic,ktd2801.yaml b/Documentation/devicetree/bindings/leds/backlight/kinetic,ktd2801.yaml
new file mode 100644
index 000000000000..b005065e0f48
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/backlight/kinetic,ktd2801.yaml
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/kinetic,ktd2801.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Kinetic Technologies KTD2801 one-wire backlight
+
+maintainers:
+  - Duje Mihanović <duje.mihanovic@skole.hr>
+
+description: |
+  The Kinetic Technologies KTD2801 is a LED backlight driver controlled
+  by a single GPIO line. The driver can be controlled with a PWM signal
+  or by pulsing the GPIO line to set the backlight level. This is called
+  "ExpressWire".
+
+allOf:
+  - $ref: common.yaml#
+
+properties:
+  compatible:
+    const: kinetic,ktd2801
+
+  ctrl-gpios:
+    maxItems: 1
+
+  default-brightness: true
+  max-brightness: true
+
+required:
+  - compatible
+  - ctrl-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    backlight {
+        compatible = "kinetic,ktd2801";
+        ctrl-gpios = <&gpio 97 GPIO_ACTIVE_HIGH>;
+        max-brightness = <210>;
+        default-brightness = <100>;
+    };

-- 
2.43.0

Re: [PATCH v2 1/2] dt-bindings: backlight: add Kinetic KTD2801 binding

[Linus Walleij]

Hi Duje,

thanks for your patch!

On Thu, Jan 18, 2024 at 6:33 PM Duje Mihanović <duje.mihanovic@skole.hr> wrote:

> Add the dt binding for the Kinetic KTD2801 backlight driver.

Maybe add some commit message?

> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
(...)
> +  ctrl-gpios:
> +    maxItems: 1

First I thought this was inconsistent with ktd253, then
I looked at the datasheets and they really did change "en" to "ctrl" so
this needs a new name indeed.

With commit message added:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

[PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Duje Mihanović]

Add driver for the Kinetic KTD2801 backlight driver.

Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>

---
Shared ExpressWire handling code and preemption watchdogs haven't been
implemented in this version as my questions regarding these two weren't
answered.
---
 MAINTAINERS                                 |   6 ++
 drivers/video/backlight/Kconfig             |   7 ++
 drivers/video/backlight/Makefile            |   1 +
 drivers/video/backlight/ktd2801-backlight.c | 149 ++++++++++++++++++++++++++++
 4 files changed, 163 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a7c4cf8201e0..1e25d760f312 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11884,6 +11884,12 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/leds/backlight/kinetic,ktd253.yaml
 F:	drivers/video/backlight/ktd253-backlight.c
 
+KTD2801 BACKLIGHT DRIVER
+M:	Duje Mihanović <duje.mihanovic@skole.hr>
+S:	Maintained
+F:	Documentation/devicetree/bindings/leds/backlight/kinetic,ktd2801.yaml
+F:	drivers/video/backlight/ktd2801-backlight.c
+
 KTEST
 M:	Steven Rostedt <rostedt@goodmis.org>
 M:	John Hawley <warthog9@eaglescrag.net>
diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index 51387b1ef012..a2b268293345 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -183,6 +183,13 @@ config BACKLIGHT_KTD253
 	  which is a 1-wire GPIO-controlled backlight found in some mobile
 	  phones.
 
+config BACKLIGHT_KTD2801
+	tristate "Backlight Driver for Kinetic KTD2801"
+	depends on GPIOLIB || COMPILE_TEST
+	help
+	  Say Y to enable the backlight driver for the Kinetic KTD2801 1-wire
+	  GPIO-controlled backlight found in Samsung Galaxy Core Prime VE LTE.
+
 config BACKLIGHT_KTZ8866
 	tristate "Backlight Driver for Kinetic KTZ8866"
 	depends on I2C
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index f72e1c3c59e9..b33b647f31ca 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_BACKLIGHT_HP680)		+= hp680_bl.o
 obj-$(CONFIG_BACKLIGHT_HP700)		+= jornada720_bl.o
 obj-$(CONFIG_BACKLIGHT_IPAQ_MICRO)	+= ipaq_micro_bl.o
 obj-$(CONFIG_BACKLIGHT_KTD253)		+= ktd253-backlight.o
+obj-$(CONFIG_BACKLIGHT_KTD2801)		+= ktd2801-backlight.o
 obj-$(CONFIG_BACKLIGHT_KTZ8866)		+= ktz8866.o
 obj-$(CONFIG_BACKLIGHT_LM3533)		+= lm3533_bl.o
 obj-$(CONFIG_BACKLIGHT_LM3630A)		+= lm3630a_bl.o
diff --git a/drivers/video/backlight/ktd2801-backlight.c b/drivers/video/backlight/ktd2801-backlight.c
new file mode 100644
index 000000000000..bbcb2e2059a2
--- /dev/null
+++ b/drivers/video/backlight/ktd2801-backlight.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+
+/* These values have been extracted from Samsung's driver. */
+#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US	150
+#define KTD2801_EXPRESSWIRE_DETECT_US		270
+#define KTD2801_LOW_BIT_HIGH_TIME_US		5
+#define KTD2801_LOW_BIT_LOW_TIME_US		(4 * KTD2801_HIGH_BIT_LOW_TIME_US)
+#define KTD2801_HIGH_BIT_LOW_TIME_US		5
+#define KTD2801_HIGH_BIT_HIGH_TIME_US		(4 * KTD2801_HIGH_BIT_LOW_TIME_US)
+#define KTD2801_DATA_START_US			5
+#define KTD2801_END_OF_DATA_LOW_US		10
+#define KTD2801_END_OF_DATA_HIGH_US		350
+#define KTD2801_PWR_DOWN_DELAY_US		2600
+
+#define KTD2801_DEFAULT_BRIGHTNESS	100
+#define KTD2801_MAX_BRIGHTNESS		255
+
+struct ktd2801_backlight {
+	struct backlight_device *bd;
+	struct gpio_desc *gpiod;
+	bool was_on;
+};
+
+static int ktd2801_update_status(struct backlight_device *bd)
+{
+	struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
+	u8 brightness = (u8) backlight_get_brightness(bd);
+
+	if (backlight_is_blank(bd)) {
+		gpiod_set_value(ktd2801->gpiod, 0);
+		udelay(KTD2801_PWR_DOWN_DELAY_US);
+		ktd2801->was_on = false;
+		return 0;
+	}
+
+	if (!ktd2801->was_on) {
+		gpiod_set_value(ktd2801->gpiod, 1);
+		udelay(KTD2801_EXPRESSWIRE_DETECT_DELAY_US);
+		gpiod_set_value(ktd2801->gpiod, 0);
+		udelay(KTD2801_EXPRESSWIRE_DETECT_US);
+		gpiod_set_value(ktd2801->gpiod, 1);
+		ktd2801->was_on = true;
+	}
+
+	gpiod_set_value(ktd2801->gpiod, 1);
+	udelay(KTD2801_DATA_START_US);
+
+	for (int i = 0; i < 8; i++) {
+		u8 next_bit = (brightness & 0x80) >> 7;
+
+		if (!next_bit) {
+			gpiod_set_value(ktd2801->gpiod, 0);
+			udelay(KTD2801_LOW_BIT_LOW_TIME_US);
+			gpiod_set_value(ktd2801->gpiod, 1);
+			udelay(KTD2801_LOW_BIT_HIGH_TIME_US);
+		} else {
+			gpiod_set_value(ktd2801->gpiod, 0);
+			udelay(KTD2801_HIGH_BIT_LOW_TIME_US);
+			gpiod_set_value(ktd2801->gpiod, 1);
+			udelay(KTD2801_HIGH_BIT_HIGH_TIME_US);
+		}
+		brightness <<= 1;
+	}
+	gpiod_set_value(ktd2801->gpiod, 0);
+	udelay(KTD2801_END_OF_DATA_LOW_US);
+	gpiod_set_value(ktd2801->gpiod, 1);
+	udelay(KTD2801_END_OF_DATA_HIGH_US);
+	return 0;
+}
+
+static const struct backlight_ops ktd2801_backlight_ops = {
+	.update_status = ktd2801_update_status,
+};
+
+static int ktd2801_backlight_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct backlight_device *bd;
+	struct ktd2801_backlight *ktd2801;
+	u32 brightness, max_brightness;
+	int ret;
+
+	ktd2801 = devm_kzalloc(dev, sizeof(*ktd2801), GFP_KERNEL);
+	if (!ktd2801)
+		return -ENOMEM;
+	ktd2801->was_on = true;
+
+	ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
+	if (ret)
+		max_brightness = KTD2801_MAX_BRIGHTNESS;
+	if (max_brightness > KTD2801_MAX_BRIGHTNESS) {
+		dev_err(dev, "illegal max brightness specified\n");
+		max_brightness = KTD2801_MAX_BRIGHTNESS;
+	}
+
+	ret = device_property_read_u32(dev, "default-brightness", &brightness);
+	if (ret)
+		brightness = KTD2801_DEFAULT_BRIGHTNESS;
+	if (brightness > max_brightness) {
+		dev_err(dev, "default brightness exceeds max\n");
+		brightness = max_brightness;
+	}
+
+	ktd2801->gpiod = devm_gpiod_get(dev, "ctrl", GPIOD_OUT_HIGH);
+	if (IS_ERR(ktd2801->gpiod))
+		return dev_err_probe(dev, PTR_ERR(dev),
+				"failed to get backlight GPIO");
+	gpiod_set_consumer_name(ktd2801->gpiod, dev_name(dev));
+
+	bd = devm_backlight_device_register(dev, dev_name(dev), dev, ktd2801,
+			&ktd2801_backlight_ops, NULL);
+	if (IS_ERR(bd))
+		return dev_err_probe(dev, PTR_ERR(bd),
+				"failed to register backlight");
+
+	bd->props.max_brightness = max_brightness;
+	bd->props.brightness = brightness;
+
+	ktd2801->bd = bd;
+	platform_set_drvdata(pdev, bd);
+	backlight_update_status(bd);
+
+	return 0;
+}
+
+static const struct of_device_id ktd2801_of_match[] = {
+	{ .compatible = "kinetic,ktd2801" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ktd2801_of_match);
+
+static struct platform_driver ktd2801_backlight_driver = {
+	.driver = {
+		.name = "ktd2801-backlight",
+		.of_match_table = ktd2801_of_match,
+	},
+	.probe = ktd2801_backlight_probe,
+};
+module_platform_driver(ktd2801_backlight_driver);
+
+MODULE_AUTHOR("Duje Mihanović <duje.mihanovic@skole.hr>");
+MODULE_DESCRIPTION("Kinetic KTD2801 Backlight Driver");
+MODULE_LICENSE("GPL");

-- 
2.43.0

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Linus Walleij]

Hi Duje,

thanks for your patch!

On Thu, Jan 18, 2024 at 6:33 PM Duje Mihanović <duje.mihanovic@skole.hr> wrote:

> Add driver for the Kinetic KTD2801 backlight driver.>
> Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>

Add some commit message?

> +#include <linux/backlight.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/of.h>

I don't think you need <linux/of.h>, the compatible table works without
that (is in the device driver core).

> +/* These values have been extracted from Samsung's driver. */
> +#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US    150
> +#define KTD2801_EXPRESSWIRE_DETECT_US          270
> +#define KTD2801_LOW_BIT_HIGH_TIME_US           5
> +#define KTD2801_LOW_BIT_LOW_TIME_US            (4 * KTD2801_HIGH_BIT_LOW_TIME_US)
> +#define KTD2801_HIGH_BIT_LOW_TIME_US           5
> +#define KTD2801_HIGH_BIT_HIGH_TIME_US          (4 * KTD2801_HIGH_BIT_LOW_TIME_US)
> +#define KTD2801_DATA_START_US                  5
> +#define KTD2801_END_OF_DATA_LOW_US             10
> +#define KTD2801_END_OF_DATA_HIGH_US            350
> +#define KTD2801_PWR_DOWN_DELAY_US              2600
> +
> +#define KTD2801_DEFAULT_BRIGHTNESS     100
> +#define KTD2801_MAX_BRIGHTNESS         255
> +
> +struct ktd2801_backlight {
> +       struct backlight_device *bd;
> +       struct gpio_desc *gpiod;
> +       bool was_on;
> +};
> +
> +static int ktd2801_update_status(struct backlight_device *bd)
> +{
> +       struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
> +       u8 brightness = (u8) backlight_get_brightness(bd);
> +
> +       if (backlight_is_blank(bd)) {
> +               gpiod_set_value(ktd2801->gpiod, 0);
> +               udelay(KTD2801_PWR_DOWN_DELAY_US);

That's 2600 us, a pretty long delay in a hard loop or delay timer!

Can you use usleep_range() instead, at least for this one?

> +       for (int i = 0; i < 8; i++) {
> +               u8 next_bit = (brightness & 0x80) >> 7;

I would just:

#include <linux/bits.h>

bool next_bit = !!(brightness & BIT(7));

Yours,
Linus Walleij

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Duje Mihanović]

On Friday, January 19, 2024 10:02:33 AM CET Linus Walleij wrote:
> Hi Duje,
> 
> thanks for your patch!
> 
> On Thu, Jan 18, 2024 at 6:33 PM Duje Mihanović <duje.mihanovic@skole.hr> 
wrote:
> > Add driver for the Kinetic KTD2801 backlight driver.>
> > Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
> 
> Add some commit message?

Besides the usual short explanation of the hardware I'd also add a link to the 
datasheet in the commit message if that's appropriate.

> > +#include <linux/backlight.h>
> > +#include <linux/delay.h>
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/of.h>
> 
> I don't think you need <linux/of.h>, the compatible table works without
> that (is in the device driver core).

Can confirm it compiles without.

> > +/* These values have been extracted from Samsung's driver. */
> > +#define KTD2801_EXPRESSWIRE_DETECT_DELAY_US    150
> > +#define KTD2801_EXPRESSWIRE_DETECT_US          270
> > +#define KTD2801_LOW_BIT_HIGH_TIME_US           5
> > +#define KTD2801_LOW_BIT_LOW_TIME_US            (4 *
> > KTD2801_HIGH_BIT_LOW_TIME_US) +#define KTD2801_HIGH_BIT_LOW_TIME_US        
> >   5
> > +#define KTD2801_HIGH_BIT_HIGH_TIME_US          (4 *
> > KTD2801_HIGH_BIT_LOW_TIME_US) +#define KTD2801_DATA_START_US               
> >   5
> > +#define KTD2801_END_OF_DATA_LOW_US             10
> > +#define KTD2801_END_OF_DATA_HIGH_US            350
> > +#define KTD2801_PWR_DOWN_DELAY_US              2600
> > +
> > +#define KTD2801_DEFAULT_BRIGHTNESS     100
> > +#define KTD2801_MAX_BRIGHTNESS         255
> > +
> > +struct ktd2801_backlight {
> > +       struct backlight_device *bd;
> > +       struct gpio_desc *gpiod;
> > +       bool was_on;
> > +};
> > +
> > +static int ktd2801_update_status(struct backlight_device *bd)
> > +{
> > +       struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
> > +       u8 brightness = (u8) backlight_get_brightness(bd);
> > +
> > +       if (backlight_is_blank(bd)) {
> > +               gpiod_set_value(ktd2801->gpiod, 0);
> > +               udelay(KTD2801_PWR_DOWN_DELAY_US);
> 
> That's 2600 us, a pretty long delay in a hard loop or delay timer!
> 
> Can you use usleep_range() instead, at least for this one?

Sounds like a good idea. Should I also make that GPIO pulldown _cansleep while 
at it?

> > +       for (int i = 0; i < 8; i++) {
> > +               u8 next_bit = (brightness & 0x80) >> 7;
> 
> I would just:
> 
> #include <linux/bits.h>
> 
> bool next_bit = !!(brightness & BIT(7));

Will do.

Regards,
--
Duje

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Daniel Thompson]

On Thu, Jan 18, 2024 at 06:32:39PM +0100, Duje Mihanović wrote:
> Add driver for the Kinetic KTD2801 backlight driver.
>
> Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
>
> ---
> Shared ExpressWire handling code and preemption watchdogs haven't been
> implemented in this version as my questions regarding these two weren't
> answered.
> ---

The last mail I saw on this topic was of the "do you have any better
ideas?" variety. I (mis)read that as "unless you have any
better ideas" and didn't realize you were waiting for anything.

I didn't have any better ideas!



Daniel.

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Duje Mihanović]

On Friday, January 19, 2024 11:07:09 AM CET Daniel Thompson wrote:
> On Thu, Jan 18, 2024 at 06:32:39PM +0100, Duje Mihanović wrote:
> > Add driver for the Kinetic KTD2801 backlight driver.
> > 
> > Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
> > 
> > ---
> > Shared ExpressWire handling code and preemption watchdogs haven't been
> > implemented in this version as my questions regarding these two weren't
> > answered.
> > ---
> 
> The last mail I saw on this topic was of the "do you have any better
> ideas?" variety. I (mis)read that as "unless you have any
> better ideas" and didn't realize you were waiting for anything.
> 
> I didn't have any better ideas!

My apologies, I'll write the library as I proposed in that email.

Regards,
--
Duje

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Christophe JAILLET]

Le 18/01/2024 à 18:32, Duje Mihanović a écrit :
> Add driver for the Kinetic KTD2801 backlight driver.
> 
> Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
> 
> ---

...

> +	ktd2801->gpiod = devm_gpiod_get(dev, "ctrl", GPIOD_OUT_HIGH);
> +	if (IS_ERR(ktd2801->gpiod))
> +		return dev_err_probe(dev, PTR_ERR(dev),

PTR_ERR(ktd2801->gpiod); ?

CJ

Re: [PATCH v2 2/2] backlight: Add Kinetic KTD2801 driver

[Duje Mihanović]

On Friday, January 19, 2024 6:29:21 PM CET Christophe JAILLET wrote:
> Le 18/01/2024 à 18:32, Duje Mihanović a écrit :
> > Add driver for the Kinetic KTD2801 backlight driver.
> > 
> > Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
> > 
> > ---
> 
> ...
> 
> > +	ktd2801->gpiod = devm_gpiod_get(dev, "ctrl", GPIOD_OUT_HIGH);
> > +	if (IS_ERR(ktd2801->gpiod))
> > +		return dev_err_probe(dev, PTR_ERR(dev),
> 
> PTR_ERR(ktd2801->gpiod); ?

Good catch, I'll fix it in v3.

Regards,
--
Duje