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>

4 files changed, 159 insertions, 21 deletions

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
new file mode 100644
index 000000000000..1e4fc727f3b1
--- /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 fa2b03750316..4c9c02216351 100644
--- 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 342b7d7cbb63..057389d69a51 100644
--- 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 63d2df43e61a..56f4a866539a 100644
--- 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);