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;
}