pwm-backlight: Add rudimentary device tree support

This commit adds very basic support for device tree probing. Currently,
only a PWM and a list of distinct brightness levels can be specified.
Enabling or disabling backlight power via GPIOs is not yet supported.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
new file mode 100644 (file)
index 0000000..1e4fc72
--- /dev/null
+++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
@@ -0,0 +1,28 @@
+pwm-backlight bindings
+
+Required properties:
+  - compatible: "pwm-backlight"
+  - pwms: OF device-tree PWM specification (see PWM binding[0])
+  - brightness-levels: Array of distinct brightness levels. Typically these
+      are in the range from 0 to 255, but any range starting at 0 will do.
+      The actual brightness level (PWM duty cycle) will be interpolated
+      from these values. 0 means a 0% duty cycle (darkest/off), while the
+      last value in the array represents a 100% duty cycle (brightest).
+  - default-brightness-level: the default brightness level (index into the
+      array defined by the "brightness-levels" property)
+
+Optional properties:
+  - pwm-names: a list of names for the PWM devices specified in the
+               "pwms" property (see PWM binding[0])
+
+[0]: Documentation/devicetree/bindings/pwm/pwm.txt
+
+Example:
+
+       backlight {
+               compatible = "pwm-backlight";
+               pwms = <&pwm 0 5000000>;
+
+               brightness-levels = <0 4 8 16 32 64 128 255>;
+               default-brightness-level = <6>;
+       };

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index fa2b03750316b175f36f72d6f7cf8cf8a69bc375..4c9c02216351e39f8f6405eaff70b454920a8dd6 100644 (file)
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -245,7 +245,7 @@ config BACKLIGHT_CARILLO_RANCH
 
 config BACKLIGHT_PWM
        tristate "Generic PWM based Backlight Driver"
-       depends on HAVE_PWM
+       depends on PWM
        help
          If you have a LCD backlight adjustable by PWM, say Y to enable
          this driver.

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 342b7d7cbb632826611f856a7eaa578220d16681..057389d69a51c5ce7d473ab45b058d9e2978fc34 100644 (file)
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -26,11 +26,13 @@ struct pwm_bl_data {
        struct device           *dev;
        unsigned int            period;
        unsigned int            lth_brightness;
+       unsigned int            *levels;
        int                     (*notify)(struct device *,
                                          int brightness);
        void                    (*notify_after)(struct device *,
                                        int brightness);
        int                     (*check_fb)(struct device *, struct fb_info *);
+       void                    (*exit)(struct device *);
 };
 
 static int pwm_backlight_update_status(struct backlight_device *bl)
@@ -52,6 +54,11 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
                pwm_config(pb->pwm, 0, pb->period);
                pwm_disable(pb->pwm);
        } else {
+               if (pb->levels) {
+                       brightness = pb->levels[brightness];
+                       max = pb->levels[max];
+               }
+
                brightness = pb->lth_brightness +
                        (brightness * (pb->period - pb->lth_brightness) / max);
                pwm_config(pb->pwm, brightness, pb->period);
@@ -83,17 +90,98 @@ static const struct backlight_ops pwm_backlight_ops = {
        .check_fb       = pwm_backlight_check_fb,
 };
 
+#ifdef CONFIG_OF
+static int pwm_backlight_parse_dt(struct device *dev,
+                                 struct platform_pwm_backlight_data *data)
+{
+       struct device_node *node = dev->of_node;
+       struct property *prop;
+       int length;
+       u32 value;
+       int ret;
+
+       if (!node)
+               return -ENODEV;
+
+       memset(data, 0, sizeof(*data));
+
+       /* determine the number of brightness levels */
+       prop = of_find_property(node, "brightness-levels", &length);
+       if (!prop)
+               return -EINVAL;
+
+       data->max_brightness = length / sizeof(u32);
+
+       /* read brightness levels from DT property */
+       if (data->max_brightness > 0) {
+               size_t size = sizeof(*data->levels) * data->max_brightness;
+
+               data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
+               if (!data->levels)
+                       return -ENOMEM;
+
+               ret = of_property_read_u32_array(node, "brightness-levels",
+                                                data->levels,
+                                                data->max_brightness);
+               if (ret < 0)
+                       return ret;
+
+               ret = of_property_read_u32(node, "default-brightness-level",
+                                          &value);
+               if (ret < 0)
+                       return ret;
+
+               if (value >= data->max_brightness) {
+                       dev_warn(dev, "invalid default brightness level: %u, using %u\n",
+                                value, data->max_brightness - 1);
+                       value = data->max_brightness - 1;
+               }
+
+               data->dft_brightness = value;
+               data->max_brightness--;
+       }
+
+       /*
+        * TODO: Most users of this driver use a number of GPIOs to control
+        *       backlight power. Support for specifying these needs to be
+        *       added.
+        */
+
+       return 0;
+}
+
+static struct of_device_id pwm_backlight_of_match[] = {
+       { .compatible = "pwm-backlight" },
+       { }
+};
+
+MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
+#else
+static int pwm_backlight_parse_dt(struct device *dev,
+                                 struct platform_pwm_backlight_data *data)
+{
+       return -ENODEV;
+}
+#endif
+
 static int pwm_backlight_probe(struct platform_device *pdev)
 {
-       struct backlight_properties props;
        struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
+       struct platform_pwm_backlight_data defdata;
+       struct backlight_properties props;
        struct backlight_device *bl;
        struct pwm_bl_data *pb;
+       unsigned int max;
        int ret;
 
        if (!data) {
-               dev_err(&pdev->dev, "failed to find platform data\n");
-               return -EINVAL;
+               ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
+               if (ret < 0) {
+                       dev_err(&pdev->dev, "failed to find platform data\n");
+                       return ret;
+               }
+
+               data = &defdata;
        }
 
        if (data->init) {
@@ -109,21 +197,42 @@ static int pwm_backlight_probe(struct platform_device *pdev)
                goto err_alloc;
        }
 
-       pb->period = data->pwm_period_ns;
+       if (data->levels) {
+               max = data->levels[data->max_brightness];
+               pb->levels = data->levels;
+       } else
+               max = data->max_brightness;
+
        pb->notify = data->notify;
        pb->notify_after = data->notify_after;
        pb->check_fb = data->check_fb;
-       pb->lth_brightness = data->lth_brightness *
-               (data->pwm_period_ns / data->max_brightness);
+       pb->exit = data->exit;
        pb->dev = &pdev->dev;
 
-       pb->pwm = pwm_request(data->pwm_id, "backlight");
+       pb->pwm = pwm_get(&pdev->dev, NULL);
        if (IS_ERR(pb->pwm)) {
-               dev_err(&pdev->dev, "unable to request PWM for backlight\n");
-               ret = PTR_ERR(pb->pwm);
-               goto err_alloc;
-       } else
-               dev_dbg(&pdev->dev, "got pwm for backlight\n");
+               dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
+
+               pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
+               if (IS_ERR(pb->pwm)) {
+                       dev_err(&pdev->dev, "unable to request legacy PWM\n");
+                       ret = PTR_ERR(pb->pwm);
+                       goto err_alloc;
+               }
+       }
+
+       dev_dbg(&pdev->dev, "got pwm for backlight\n");
+
+       /*
+        * The DT case will set the pwm_period_ns field to 0 and store the
+        * period, parsed from the DT, in the PWM device. For the non-DT case,
+        * set the period from platform data.
+        */
+       if (data->pwm_period_ns > 0)
+               pwm_set_period(pb->pwm, data->pwm_period_ns);
+
+       pb->period = pwm_get_period(pb->pwm);
+       pb->lth_brightness = data->lth_brightness * (pb->period / max);
 
        memset(&props, 0, sizeof(struct backlight_properties));
        props.type = BACKLIGHT_RAW;
@@ -143,7 +252,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
        return 0;
 
 err_bl:
-       pwm_free(pb->pwm);
+       pwm_put(pb->pwm);
 err_alloc:
        if (data->exit)
                data->exit(&pdev->dev);
@@ -152,16 +261,15 @@ err_alloc:
 
 static int pwm_backlight_remove(struct platform_device *pdev)
 {
-       struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
        struct backlight_device *bl = platform_get_drvdata(pdev);
        struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
 
        backlight_device_unregister(bl);
        pwm_config(pb->pwm, 0, pb->period);
        pwm_disable(pb->pwm);
-       pwm_free(pb->pwm);
-       if (data->exit)
-               data->exit(&pdev->dev);
+       pwm_put(pb->pwm);
+       if (pb->exit)
+               pb->exit(&pdev->dev);
        return 0;
 }
 
@@ -195,11 +303,12 @@ static SIMPLE_DEV_PM_OPS(pwm_backlight_pm_ops, pwm_backlight_suspend,
 
 static struct platform_driver pwm_backlight_driver = {
        .driver         = {
-               .name   = "pwm-backlight",
-               .owner  = THIS_MODULE,
+               .name           = "pwm-backlight",
+               .owner          = THIS_MODULE,
 #ifdef CONFIG_PM
-               .pm     = &pwm_backlight_pm_ops,
+               .pm             = &pwm_backlight_pm_ops,
 #endif
+               .of_match_table = of_match_ptr(pwm_backlight_of_match),
        },
        .probe          = pwm_backlight_probe,
        .remove         = pwm_backlight_remove,

diff --git a/include/linux/pwm_backlight.h b/include/linux/pwm_backlight.h
index 63d2df43e61a1999206d15b6d06f3567b9ac8f9e..56f4a866539ad7b66476fc3d1c09d15ab8ad2be1 100644 (file)
--- a/include/linux/pwm_backlight.h
+++ b/include/linux/pwm_backlight.h
@@ -12,6 +12,7 @@ struct platform_pwm_backlight_data {
        unsigned int dft_brightness;
        unsigned int lth_brightness;
        unsigned int pwm_period_ns;
+       unsigned int *levels;
        int (*init)(struct device *dev);
        int (*notify)(struct device *dev, int brightness);
        void (*notify_after)(struct device *dev, int brightness);