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author | Martin Blumenstingl <martin.blumenstingl@googlemail.com> | 2019-06-12 21:59:10 +0200 |
---|---|---|
committer | Thierry Reding <thierry.reding@gmail.com> | 2019-06-26 11:39:10 +0200 |
commit | 7341c785d81ebf5472462b7f8ee27a96a59d5cf4 (patch) | |
tree | d5157551694c40a3312909db5c139248ea13f709 /drivers/pwm/pwm-meson.c | |
parent | d6885b3e0a39ba7f93d4dc77ed9112e44a09b40d (diff) | |
download | linux-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/pwm/pwm-meson.c')
-rw-r--r-- | drivers/pwm/pwm-meson.c | 23 |
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) |