* [PATCH v2 1/2] backlight: pwm_bl: Configure pwm only once per backlight toggle
2023-01-20 12:00 [PATCH v2 0/2] backlight: pwm_bl: Two PWM releated changes Uwe Kleine-König
@ 2023-01-20 12:00 ` Uwe Kleine-König
2023-01-20 17:07 ` Lee Jones
2023-01-20 12:00 ` [PATCH v2 2/2] backlight: pwm_bl: Don't rely on a disabled PWM emiting inactive state Uwe Kleine-König
1 sibling, 1 reply; 6+ messages in thread
From: Uwe Kleine-König @ 2023-01-20 12:00 UTC (permalink / raw)
To: Lee Jones, Daniel Thompson, Jingoo Han
Cc: Thierry Reding, Helge Deller, linux-pwm, dri-devel, linux-fbdev,
kernel
When the function pwm_backlight_update_status() was called with
brightness > 0, pwm_get_state() was called twice (once directly and once
in compute_duty_cycle). Also pwm_apply_state() was called twice (once in
pwm_backlight_power_on() and once directly).
Optimize this to do both calls only once.
Note that with this affects the order of regulator and PWM setup. It's
not expected to have a relevant effect on hardware. The rationale for
this is that the regulator (and the GPIO) are reasonable to switch in
pwm_backlight_power_on()/pwm_backlight_power_off() but the PWM has
nothing to do with power. (The post_pwm_on_delay and pwm_off_delay are
still there though.)
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
drivers/video/backlight/pwm_bl.c | 28 ++++++++++------------------
1 file changed, 10 insertions(+), 18 deletions(-)
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index d0b22158cd70..0509fecd5715 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -40,10 +40,8 @@ struct pwm_bl_data {
static void pwm_backlight_power_on(struct pwm_bl_data *pb)
{
- struct pwm_state state;
int err;
- pwm_get_state(pb->pwm, &state);
if (pb->enabled)
return;
@@ -51,9 +49,6 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
if (err < 0)
dev_err(pb->dev, "failed to enable power supply\n");
- state.enabled = true;
- pwm_apply_state(pb->pwm, &state);
-
if (pb->post_pwm_on_delay)
msleep(pb->post_pwm_on_delay);
@@ -65,9 +60,6 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
static void pwm_backlight_power_off(struct pwm_bl_data *pb)
{
- struct pwm_state state;
-
- pwm_get_state(pb->pwm, &state);
if (!pb->enabled)
return;
@@ -77,28 +69,21 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
if (pb->pwm_off_delay)
msleep(pb->pwm_off_delay);
- state.enabled = false;
- state.duty_cycle = 0;
- pwm_apply_state(pb->pwm, &state);
-
regulator_disable(pb->power_supply);
pb->enabled = false;
}
-static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
+static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state)
{
unsigned int lth = pb->lth_brightness;
- struct pwm_state state;
u64 duty_cycle;
- pwm_get_state(pb->pwm, &state);
-
if (pb->levels)
duty_cycle = pb->levels[brightness];
else
duty_cycle = brightness;
- duty_cycle *= state.period - lth;
+ duty_cycle *= state->period - lth;
do_div(duty_cycle, pb->scale);
return duty_cycle + lth;
@@ -115,11 +100,18 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
if (brightness > 0) {
pwm_get_state(pb->pwm, &state);
- state.duty_cycle = compute_duty_cycle(pb, brightness);
+ state.duty_cycle = compute_duty_cycle(pb, brightness, &state);
+ state.enabled = true;
pwm_apply_state(pb->pwm, &state);
+
pwm_backlight_power_on(pb);
} else {
pwm_backlight_power_off(pb);
+
+ pwm_get_state(pb->pwm, &state);
+ state.enabled = false;
+ state.duty_cycle = 0;
+ pwm_apply_state(pb->pwm, &state);
}
if (pb->notify_after)
--
2.39.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH v2 2/2] backlight: pwm_bl: Don't rely on a disabled PWM emiting inactive state
2023-01-20 12:00 [PATCH v2 0/2] backlight: pwm_bl: Two PWM releated changes Uwe Kleine-König
2023-01-20 12:00 ` [PATCH v2 1/2] backlight: pwm_bl: Configure pwm only once per backlight toggle Uwe Kleine-König
@ 2023-01-20 12:00 ` Uwe Kleine-König
2023-01-20 15:04 ` Daniel Thompson
2023-01-20 17:07 ` Lee Jones
1 sibling, 2 replies; 6+ messages in thread
From: Uwe Kleine-König @ 2023-01-20 12:00 UTC (permalink / raw)
To: Lee Jones, Daniel Thompson, Jingoo Han, Liam Girdwood, Mark Brown
Cc: Thierry Reding, Helge Deller, linux-pwm, dri-devel, linux-fbdev,
kernel
Most but not all PWMs drive the PWM pin to its inactive state when
disabled. However if there is no enable_gpio and no regulator the PWM
must drive the inactive state to actually disable the backlight.
So keep the PWM on in this case.
Note that to determine if there is a regulator some effort is required
because it might happen that there isn't actually one but the regulator
core gave us a dummy. (A nice side effect is that this makes the
regulator actually optional even on fully constrained systems.)
This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is
used.
Hint for the future: If this change results in a regression, the bug is
in the lowlevel PWM driver.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
drivers/video/backlight/pwm_bl.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 0509fecd5715..fb388148d98f 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -45,9 +45,11 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
if (pb->enabled)
return;
- err = regulator_enable(pb->power_supply);
- if (err < 0)
- dev_err(pb->dev, "failed to enable power supply\n");
+ if (pb->power_supply) {
+ err = regulator_enable(pb->power_supply);
+ if (err < 0)
+ dev_err(pb->dev, "failed to enable power supply\n");
+ }
if (pb->post_pwm_on_delay)
msleep(pb->post_pwm_on_delay);
@@ -69,7 +71,8 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
if (pb->pwm_off_delay)
msleep(pb->pwm_off_delay);
- regulator_disable(pb->power_supply);
+ if (pb->power_supply)
+ regulator_disable(pb->power_supply);
pb->enabled = false;
}
@@ -109,8 +112,16 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
pwm_backlight_power_off(pb);
pwm_get_state(pb->pwm, &state);
- state.enabled = false;
state.duty_cycle = 0;
+ /*
+ * We cannot assume a disabled PWM to drive its output to the
+ * inactive state. If we have an enable GPIO and/or a regulator
+ * we assume that this isn't relevant and we can disable the PWM
+ * to save power. If however there is neither an enable GPIO nor
+ * a regulator keep the PWM on be sure to get a constant
+ * inactive output.
+ */
+ state.enabled = !pb->power_supply && !pb->enable_gpio;
pwm_apply_state(pb->pwm, &state);
}
@@ -408,7 +419,7 @@ static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
active = false;
- if (!regulator_is_enabled(pb->power_supply))
+ if (pb->power_supply && !regulator_is_enabled(pb->power_supply))
active = false;
if (!pwm_is_enabled(pb->pwm))
@@ -489,10 +500,13 @@ static int pwm_backlight_probe(struct platform_device *pdev)
goto err_alloc;
}
- pb->power_supply = devm_regulator_get(&pdev->dev, "power");
+ pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power");
if (IS_ERR(pb->power_supply)) {
ret = PTR_ERR(pb->power_supply);
- goto err_alloc;
+ if (ret == -ENODEV)
+ pb->power_supply = NULL;
+ else
+ goto err_alloc;
}
pb->pwm = devm_pwm_get(&pdev->dev, NULL);
--
2.39.0
^ permalink raw reply related [flat|nested] 6+ messages in thread