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 318dce7..4df15f0 100644
--- a/drivers/pwm/sandbox_pwm.c
+++ b/drivers/pwm/sandbox_pwm.c
@@ -59,8 +59,15 @@
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 9e32bc4..4c86215 100644
--- a/drivers/video/pwm_backlight.c
+++ b/drivers/video/pwm_backlight.c
@@ -62,10 +62,17 @@
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 @@
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];