video: backlight: Support PWMs without a known period_ns

The PWM device provided by Chrome OS EC doesn't really support anything
other than setting a relative duty cycle. To support it as a backlight,
this patch makes the PWM period optional in the device tree and pretends
the valid brightness range is its period_ns.

Also adds a sandbox test for a PWM channel that has a fixed period,
checking that the resulting duty_cycle matches on a set_config() even if
the requested period_ns can't be set.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/drivers/pwm/sandbox_pwm.c b/drivers/pwm/sandbox_pwm.c
index 318dce7c14905805614cc7485d533d2ef31e6084..4df15f0a2e8fbfa76e1d39cd6ce935d36f897f22 100644 (file)
--- a/drivers/pwm/sandbox_pwm.c
+++ b/drivers/pwm/sandbox_pwm.c
@@ -59,8 +59,15 @@ static int sandbox_pwm_set_config(struct udevice *dev, uint channel,
        if (channel >= NUM_CHANNELS)
                return -ENOSPC;
        chan = &priv->chan[channel];
-       chan->period_ns = period_ns;
-       chan->duty_ns = duty_ns;
+
+       if (channel == 2) {
+               /* Pretend to have some fixed period */
+               chan->period_ns = 4096;
+               chan->duty_ns =  duty_ns * 4096 / period_ns;
+       } else {
+               chan->period_ns = period_ns;
+               chan->duty_ns = duty_ns;
+       }
 
        return 0;
 }

diff --git a/drivers/video/pwm_backlight.c b/drivers/video/pwm_backlight.c
index 9e32bc47cffbf979fd4f160fa458c39947866eb1..4c86215bd73e57c29883fe9e6ff976f229eb5f8a 100644 (file)
--- a/drivers/video/pwm_backlight.c
+++ b/drivers/video/pwm_backlight.c
@@ -62,10 +62,17 @@ static int set_pwm(struct pwm_backlight_priv *priv)
        uint duty_cycle;
        int ret;
 
-       duty_cycle = priv->period_ns * (priv->cur_level - priv->min_level) /
-               (priv->max_level - priv->min_level);
-       ret = pwm_set_config(priv->pwm, priv->channel, priv->period_ns,
-                            duty_cycle);
+       if (priv->period_ns) {
+               duty_cycle = priv->period_ns * (priv->cur_level - priv->min_level) /
+                       (priv->max_level - priv->min_level);
+               ret = pwm_set_config(priv->pwm, priv->channel, priv->period_ns,
+                                    duty_cycle);
+       } else {
+               /* PWM driver will internally scale these like the above. */
+               ret = pwm_set_config(priv->pwm, priv->channel,
+                                    priv->max_level - priv->min_level,
+                                    priv->cur_level - priv->min_level);
+       }
        if (ret)
                return log_ret(ret);
 
@@ -213,10 +220,11 @@ static int pwm_backlight_of_to_plat(struct udevice *dev)
                log_debug("Cannot get PWM: ret=%d\n", ret);
                return log_ret(ret);
        }
-       if (args.args_count < 2)
+       if (args.args_count < 1)
                return log_msg_ret("Not enough arguments to pwm\n", -EINVAL);
        priv->channel = args.args[0];
-       priv->period_ns = args.args[1];
+       if (args.args_count > 1)
+               priv->period_ns = args.args[1];
        if (args.args_count > 2)
                priv->polarity = args.args[2];
 

diff --git a/include/pwm.h b/include/pwm.h
index f9959706ceb696536af9bfeb1cc3748e2dd6b28a..668551e4b8a9a74a1074a474c2ded755459c885a 100644 (file)
--- a/include/pwm.h
+++ b/include/pwm.h
@@ -17,6 +17,10 @@ struct pwm_ops {
        /**
         * set_config() - Set the PWM configuration
         *
+        * Change both the PWM device's period and it's duty period if
+        * possible. Otherwise, set an appropriate duty period that best
+        * matches the given period_ns / duty_ns ratio for the device.
+        *
         * @dev:        PWM device to update
         * @channel:    PWM channel to update
         * @period_ns:  PWM period in nanoseconds
@@ -51,6 +55,10 @@ struct pwm_ops {
 /**
  * pwm_set_config() - Set the PWM configuration
  *
+ * Change both the PWM device's period and it's duty period if
+ * possible. Otherwise, set an appropriate duty period that best
+ * matches the given period_ns / duty_ns ratio for the device.
+ *
  * @dev:       PWM device to update
  * @channel:   PWM channel to update
  * @period_ns: PWM period in nanoseconds

diff --git a/test/dm/pwm.c b/test/dm/pwm.c
index 0de6dba1ba64ab52102d8ae7453f9d2725333bec..b624cf3d6558a788091884c3ebc3fe6b2468729f 100644 (file)
--- a/test/dm/pwm.c
+++ b/test/dm/pwm.c
@@ -6,6 +6,7 @@
 #include <common.h>
 #include <dm.h>
 #include <pwm.h>
+#include <asm/test.h>
 #include <dm/test.h>
 #include <test/test.h>
 #include <test/ut.h>
@@ -14,6 +15,10 @@
 static int dm_test_pwm_base(struct unit_test_state *uts)
 {
        struct udevice *dev;
+       uint period_ns;
+       uint duty_ns;
+       bool enable;
+       bool polarity;
 
        ut_assertok(uclass_get_device(UCLASS_PWM, 0, &dev));
        ut_assertnonnull(dev);
@@ -24,6 +29,12 @@ static int dm_test_pwm_base(struct unit_test_state *uts)
        ut_asserteq(-ENOSPC, pwm_set_enable(dev, 3, true));
        ut_assertok(pwm_set_invert(dev, 0, true));
 
+       ut_assertok(pwm_set_config(dev, 2, 100, 50));
+       ut_assertok(sandbox_pwm_get_config(dev, 2, &period_ns, &duty_ns,
+                                          &enable, &polarity));
+       ut_asserteq(period_ns, 4096);
+       ut_asserteq(duty_ns, 50 * 4096 / 100);
+
        ut_assertok(uclass_get_device(UCLASS_PWM, 1, &dev));
        ut_asserteq(-ENODEV, uclass_get_device(UCLASS_PWM, 2, &dev));