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authorMartin Blumenstingl <martin.blumenstingl@googlemail.com>2019-06-12 21:59:10 +0200
committerThierry Reding <thierry.reding@gmail.com>2019-06-26 11:39:10 +0200
commit7341c785d81ebf5472462b7f8ee27a96a59d5cf4 (patch)
treed5157551694c40a3312909db5c139248ea13f709 /drivers
parentd6885b3e0a39ba7f93d4dc77ed9112e44a09b40d (diff)
downloadlinux-7341c785d81ebf5472462b7f8ee27a96a59d5cf4.tar.bz2
pwm: meson: Add support PWM_POLARITY_INVERSED when disabling
meson_pwm_apply() has to consider the PWM polarity when disabling the output. With enabled=false and polarity=PWM_POLARITY_NORMAL the output needs to be LOW. The driver already supports this. With enabled=false and polarity=PWM_POLARITY_INVERSED the output needs to be HIGH. Implement this in the driver by internally enabling the output with the same settings that we already use for "period == duty". This fixes a PWM API violation which expects that the driver honors the polarity also for enabled=false. Due to the IP block not supporting this natively we only get "an as close as possible" to 100% HIGH signal (in my test setup with input clock of 24MHz and measuring the output with a logic analyzer at 24MHz sampling rate I got a duty cycle of 99.998475% on a Khadas VIM). Reviewed-by: Neil Armstrong <narmstrong@baylibre.com> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/pwm/pwm-meson.c23
1 files changed, 22 insertions, 1 deletions
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 70a8ca3409b7..f934828aaff9 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -245,6 +245,7 @@ static void meson_pwm_disable(struct meson_pwm *meson, struct pwm_device *pwm)
static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
struct pwm_state *state)
{
+ struct meson_pwm_channel *channel = pwm_get_chip_data(pwm);
struct meson_pwm *meson = to_meson_pwm(chip);
int err = 0;
@@ -252,7 +253,27 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
return -EINVAL;
if (!state->enabled) {
- meson_pwm_disable(meson, pwm);
+ if (state->polarity == PWM_POLARITY_INVERSED) {
+ /*
+ * This IP block revision doesn't have an "always high"
+ * setting which we can use for "inverted disabled".
+ * Instead we achieve this using the same settings
+ * that we use a pre_div of 0 (to get the shortest
+ * possible duration for one "count") and
+ * "period == duty_cycle". This results in a signal
+ * which is LOW for one "count", while being HIGH for
+ * the rest of the (so the signal is HIGH for slightly
+ * less than 100% of the period, but this is the best
+ * we can achieve).
+ */
+ channel->pre_div = 0;
+ channel->hi = ~0;
+ channel->lo = 0;
+
+ meson_pwm_enable(meson, pwm);
+ } else {
+ meson_pwm_disable(meson, pwm);
+ }
} else {
err = meson_pwm_calc(meson, pwm, state);
if (err < 0)