From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: linux-amlogic@lists.infradead.org, linux-pwm@vger.kernel.org,
thierry.reding@gmail.com
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
u.kleine-koenig@pengutronix.de, narmstrong@baylibre.com,
Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Subject: [PATCH v3 13/14] pwm: meson: add support PWM_POLARITY_INVERSED when disabling
Date: Wed, 12 Jun 2019 21:59:10 +0200 [thread overview]
Message-ID: <20190612195911.4442-14-martin.blumenstingl@googlemail.com> (raw)
In-Reply-To: <20190612195911.4442-1-martin.blumenstingl@googlemail.com>
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>
---
drivers/pwm/pwm-meson.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 900d362ec3c9..bb48ba85f756 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)
--
2.22.0
next prev parent reply other threads:[~2019-06-12 19:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 19:58 [PATCH v3 00/14] pwm-meson: cleanups and improvements Martin Blumenstingl
2019-06-12 19:58 ` [PATCH v3 01/14] pwm: meson: unify the parameter list of meson_pwm_{enable,disable} Martin Blumenstingl
2019-06-12 19:58 ` [PATCH v3 02/14] pwm: meson: use devm_clk_get_optional() to get the input clock Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 03/14] pwm: meson: use GENMASK and FIELD_PREP for the lo and hi values Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 04/14] pwm: meson: change MISC_CLK_SEL_WIDTH to MISC_CLK_SEL_MASK Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 05/14] pwm: meson: don't duplicate the polarity internally Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 06/14] pwm: meson: pass struct pwm_device to meson_pwm_calc() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 07/14] pwm: meson: add the meson_pwm_channel data to struct meson_pwm Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 08/14] pwm: meson: add the per-channel register offsets and bits in a struct Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 09/14] pwm: meson: move pwm_set_chip_data() to meson_pwm_request() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 10/14] pwm: meson: simplify the calculation of the pre-divider and count Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 11/14] pwm: meson: read the full hardware state in meson_pwm_get_state() Martin Blumenstingl
2019-06-12 19:59 ` [PATCH v3 12/14] pwm: meson: don't cache struct pwm_state internally Martin Blumenstingl
2019-06-12 19:59 ` Martin Blumenstingl [this message]
2019-06-12 19:59 ` [PATCH v3 14/14] pwm: meson: add documentation to the driver Martin Blumenstingl
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