[PATCH v2 0/2] backlight_lm3630a: add enable_gpios property

To be able to handle the HWEN pin of the lm3630a, add
an enable gpio to the driver and a property.

Tested on Kobo Clara HD.

Changes in v2:
simplification and reordering

Andreas Kemnade (2):
  dt-bindings: backlight: lm3630a: add enable_gpios
  backlight: lm3630a: add an enable gpio for the HWEN pin

 .../bindings/leds/backlight/lm3630a-backlight.yaml     |  5 +++++
 drivers/video/backlight/lm3630a_bl.c                   | 10 ++++++++++
 2 files changed, 15 insertions(+)

-- 
2.20.1

add enable-gpios to describe HWEN pin

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
changes in v2: add example
 .../bindings/leds/backlight/lm3630a-backlight.yaml           | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
index dc129d9a329e..1fa83feffe16 100644
--- a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
+++ b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml

@@ -29,6 +29,10 @@ properties:
   '#size-cells':
     const: 0
 
+  enable-gpios:
+    description: GPIO to use to enable/disable the backlight (HWEN pin).
+    maxItems: 1
+
 required:
   - compatible
   - reg

@@ -92,6 +96,7 @@ examples:
     i2c {
         #address-cells = <1>;
         #size-cells = <0>;
+        enable-gpios = <&gpio2 5 GPIO_ACTIVE_HIGH>;
 
         led-controller@38 {
                 compatible = "ti,lm3630a";

-- 
2.20.1

For now just enable it in the probe function to allow i2c
access. Disabling also means resetting the register values
to default and according to the datasheet does not give
power savings

Tested on Kobo Clara HD.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
changes in v2:
- simplification
- correct gpio direction initialisation

 drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 8f84f3684f04..9d0639d4202d 100644
--- a/drivers/video/backlight/lm3630a_bl.c
+++ b/drivers/video/backlight/lm3630a_bl.c

@@ -12,6 +12,8 @@
 #include <linux/uaccess.h>
 #include <linux/interrupt.h>
 #include <linux/regmap.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio.h>
 #include <linux/pwm.h>
 #include <linux/platform_data/lm3630a_bl.h>
 

@@ -48,6 +50,7 @@ struct lm3630a_chip {
 	struct lm3630a_platform_data *pdata;
 	struct backlight_device *bleda;
 	struct backlight_device *bledb;
+	struct gpio_desc *enable_gpio;
 	struct regmap *regmap;
 	struct pwm_device *pwmd;
 };

@@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
 	}
 	pchip->pdata = pdata;
 
+	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(pchip->enable_gpio)) {
+		rval = PTR_ERR(pchip->enable_gpio);
+		return rval;
+	}
+
 	/* chip initialize */
 	rval = lm3630a_chip_init(pchip);
 	if (rval < 0) {

-- 
2.20.1

On Tue, Sep 10, 2019 at 11:29:08PM +0200, Andreas Kemnade wrote:

add enable-gpios to describe HWEN pin

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>

Acked-by: Daniel Thompson <redacted>

On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:

Nitpicking... but I don't think linux/gpio.h is used anymore.

Andreas

On 9/11/19 5:08 AM, Daniel Thompson wrote:

On Tue, Sep 10, 2019 at 11:29:08PM +0200, Andreas Kemnade wrote:

quoted

add enable-gpios to describe HWEN pin

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>

Acked-by: Daniel Thompson <redacted>

quoted

---
changes in v2: add example
  .../bindings/leds/backlight/lm3630a-backlight.yaml           | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
index dc129d9a329e..1fa83feffe16 100644
--- a/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml
+++ b/Documentation/devicetree/bindings/leds/backlight/lm3630a-backlight.yaml

@@ -29,6 +29,10 @@ properties:
    '#size-cells':
      const: 0
  
+  enable-gpios:
+    description: GPIO to use to enable/disable the backlight (HWEN pin).
+    maxItems: 1
+
  required:
    - compatible
    - reg

@@ -92,6 +96,7 @@ examples:
      i2c {
          #address-cells = <1>;
          #size-cells = <0>;
+        enable-gpios = <&gpio2 5 GPIO_ACTIVE_HIGH>;

This is in the wrong place.  This is implying that the gpio is for the 
i2c parent

This needs to go under the led-controller node below

Dan

quoted

  
          led-controller@38 {
                  compatible = "ti,lm3630a";
-- 
2.20.1

On 9/11/19 5:25 AM, Daniel Thompson wrote:

On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:

quoted

For now just enable it in the probe function to allow i2c
access. Disabling also means resetting the register values
to default and according to the datasheet does not give
power savings

Tested on Kobo Clara HD.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
changes in v2:
- simplification
- correct gpio direction initialisation

  drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 8f84f3684f04..9d0639d4202d 100644
--- a/drivers/video/backlight/lm3630a_bl.c
+++ b/drivers/video/backlight/lm3630a_bl.c

@@ -12,6 +12,8 @@
  #include <linux/uaccess.h>
  #include <linux/interrupt.h>
  #include <linux/regmap.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio.h>

Nitpicking... but I don't think linux/gpio.h is used anymore.

quoted

  #include <linux/pwm.h>
  #include <linux/platform_data/lm3630a_bl.h>
  

@@ -48,6 +50,7 @@ struct lm3630a_chip {
  	struct lm3630a_platform_data *pdata;
  	struct backlight_device *bleda;
  	struct backlight_device *bledb;
+	struct gpio_desc *enable_gpio;
  	struct regmap *regmap;
  	struct pwm_device *pwmd;
  };

@@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
  	}
  	pchip->pdata = pdata;
  
+	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(pchip->enable_gpio)) {
+		rval = PTR_ERR(pchip->enable_gpio);
+		return rval;

the enable gpio is optional so if it fails you log the error and move on

Also on driver removal did you want to set the GPIO to low to disable 
the device to save power?

Dan

quoted

+	}
+
  	/* chip initialize */
  	rval = lm3630a_chip_init(pchip);
  	if (rval < 0) {
-- 
2.20.1

On Wed, 11 Sep 2019 13:48:36 -0500
Dan Murphy [off-list ref] wrote:

quoted

quoted

@@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
  	}
  	pchip->pdata = pdata;
  
+	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(pchip->enable_gpio)) {
+		rval = PTR_ERR(pchip->enable_gpio);
+		return rval;  

the enable gpio is optional so if it fails you log the error and move on

well, if the gpio is not there, then it returns NULL.
It might return e.g. -EDEFER. So I need to check for errors here.
 

Also on driver removal did you want to set the GPIO to low to disable 
the device to save power?

page 5 of the datasheet says:

Ishdn = Typ. 1µA max. 4µA.
For HWEN=Vin, I2c shutdown  (I guess this means outputs powered off)
ond for HWEN=GND.

So are we really saving something here?

Regards,
Andreas

On Wed, Sep 11, 2019 at 01:48:36PM -0500, Dan Murphy wrote:

On 9/11/19 5:25 AM, Daniel Thompson wrote:

quoted

On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:

quoted

For now just enable it in the probe function to allow i2c
access. Disabling also means resetting the register values
to default and according to the datasheet does not give
power savings

Tested on Kobo Clara HD.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
changes in v2:
- simplification
- correct gpio direction initialisation

  drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 8f84f3684f04..9d0639d4202d 100644
--- a/drivers/video/backlight/lm3630a_bl.c
+++ b/drivers/video/backlight/lm3630a_bl.c

@@ -12,6 +12,8 @@
  #include <linux/uaccess.h>
  #include <linux/interrupt.h>
  #include <linux/regmap.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio.h>

Nitpicking... but I don't think linux/gpio.h is used anymore.

quoted

  #include <linux/pwm.h>
  #include <linux/platform_data/lm3630a_bl.h>

@@ -48,6 +50,7 @@ struct lm3630a_chip {
  	struct lm3630a_platform_data *pdata;
  	struct backlight_device *bleda;
  	struct backlight_device *bledb;
+	struct gpio_desc *enable_gpio;
  	struct regmap *regmap;
  	struct pwm_device *pwmd;
  };

@@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
  	}
  	pchip->pdata = pdata;
+	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(pchip->enable_gpio)) {
+		rval = PTR_ERR(pchip->enable_gpio);
+		return rval;

the enable gpio is optional so if it fails you log the error and move on

Isn't the effect of this to cope gracefully if enable-gpios is absent
but to fail with an error if enable-gpios exists and is broken. I
thought this code pattern is fairly common.

Also on driver removal did you want to set the GPIO to low to disable the
device to save power?

As it happens I offered to opposite feedback for v1:
https://lists.freedesktop.org/archives/dri-devel/2019-September/234918.html

Basically if the power matters then we should take care of things in the
PM code path (which for this driver means reacting properly to
suspended flag when updating the brightness). If the power doesn't matter
then, given unallocated GPIO pins are in an unknown state anyway, there
is no point in tidying up because we don't know what value to restore.


Daniel.