| Message ID | 1509022186-19636-4-git-send-email-LW@KARO-electronics.de |
|---|---|
| State | Superseded |
| Headers | show |
| Series | backlight: pwm_bl: prevent backlight flicker when switching PWM on | expand |
On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > When switching the backlight on, the LCD may need some time to adjust > to the configured PWM duty cycle. Add a configurable delay between > configuring the PWM and enabling the backlight regulator to account > for this. > > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> > --- > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > 2 files changed, 23 insertions(+), 3 deletions(-) > > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > index 764db86..95594c3 100644 > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > @@ -17,6 +17,10 @@ Optional properties: > "pwms" property (see PWM binding[0]) > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > and disables the backlight (see GPIO binding[1]) > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > + and switching PWM on. This may be required to eliminate > + flicker when switching the PWM on after it has been > + disabled. The subject talks about turning on the backlight regulator, but this only talks about the PWM. > > [0]: Documentation/devicetree/bindings/pwm/pwm.txt > [1]: Documentation/devicetree/bindings/gpio/gpio.txt -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 27 Oct 2017, Rob Herring wrote: > On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > > When switching the backlight on, the LCD may need some time to adjust > > to the configured PWM duty cycle. Add a configurable delay between > > configuring the PWM and enabling the backlight regulator to account > > for this. > > > > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> > > --- > > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > > 2 files changed, 23 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > index 764db86..95594c3 100644 > > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > @@ -17,6 +17,10 @@ Optional properties: > > "pwms" property (see PWM binding[0]) > > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > > and disables the backlight (see GPIO binding[1]) > > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > > + and switching PWM on. This may be required to eliminate > > + flicker when switching the PWM on after it has been > > + disabled. > > The subject talks about turning on the backlight regulator, but this > only talks about the PWM. From my understanding "switching PWM on" == enabling the regulator. I don't see any disparity here. Or am I missing something? > > [0]: Documentation/devicetree/bindings/pwm/pwm.txt > > [1]: Documentation/devicetree/bindings/gpio/gpio.txt
On Mon, Oct 30, 2017 at 5:33 AM, Lee Jones <lee.jones@linaro.org> wrote: > On Fri, 27 Oct 2017, Rob Herring wrote: > >> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: >> > When switching the backlight on, the LCD may need some time to adjust >> > to the configured PWM duty cycle. Add a configurable delay between >> > configuring the PWM and enabling the backlight regulator to account >> > for this. >> > >> > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> >> > --- >> > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ >> > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- >> > 2 files changed, 23 insertions(+), 3 deletions(-) >> > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> > index 764db86..95594c3 100644 >> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> > @@ -17,6 +17,10 @@ Optional properties: >> > "pwms" property (see PWM binding[0]) >> > - enable-gpios: contains a single GPIO specifier for the GPIO which enables >> > and disables the backlight (see GPIO binding[1]) >> > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM >> > + and switching PWM on. This may be required to eliminate >> > + flicker when switching the PWM on after it has been >> > + disabled. >> >> The subject talks about turning on the backlight regulator, but this >> only talks about the PWM. > > From my understanding "switching PWM on" == enabling the regulator. > > I don't see any disparity here. Or am I missing something? The delay is from (re-)enabling the PWM (turning it on) to switching backlight power on. That sounds like 2 different things to me. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On Tue, 7 Nov 2017 18:46:18 -0600 Rob Herring wrote: > On Mon, Oct 30, 2017 at 5:33 AM, Lee Jones <lee.jones@linaro.org> wrote: > > On Fri, 27 Oct 2017, Rob Herring wrote: > > > >> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > >> > When switching the backlight on, the LCD may need some time to adjust > >> > to the configured PWM duty cycle. Add a configurable delay between > >> > configuring the PWM and enabling the backlight regulator to account > >> > for this. > >> > > >> > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> > >> > --- > >> > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > >> > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > >> > 2 files changed, 23 insertions(+), 3 deletions(-) > >> > > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > index 764db86..95594c3 100644 > >> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > @@ -17,6 +17,10 @@ Optional properties: > >> > "pwms" property (see PWM binding[0]) > >> > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > >> > and disables the backlight (see GPIO binding[1]) > >> > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > >> > + and switching PWM on. This may be required to eliminate > >> > + flicker when switching the PWM on after it has been > >> > + disabled. > >> > >> The subject talks about turning on the backlight regulator, but this > >> only talks about the PWM. > > > > From my understanding "switching PWM on" == enabling the regulator. > > > > I don't see any disparity here. Or am I missing something? > > The delay is from (re-)enabling the PWM (turning it on) to switching > backlight power on. That sounds like 2 different things to me. > The text should better read: + - turn-on-delay-ms: delay in milliseconds between configuring the PWM + and switching the backlight regulator on. This may be + required to eliminate flicker when switching the backlight + on after it had been disabled. Lothar Waßmann -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 08 Nov 2017, Lothar Waßmann wrote: > Hi, > > On Tue, 7 Nov 2017 18:46:18 -0600 Rob Herring wrote: > > On Mon, Oct 30, 2017 at 5:33 AM, Lee Jones <lee.jones@linaro.org> wrote: > > > On Fri, 27 Oct 2017, Rob Herring wrote: > > > > > >> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > > >> > When switching the backlight on, the LCD may need some time to adjust > > >> > to the configured PWM duty cycle. Add a configurable delay between > > >> > configuring the PWM and enabling the backlight regulator to account > > >> > for this. > > >> > > > >> > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> > > >> > --- > > >> > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > > >> > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > > >> > 2 files changed, 23 insertions(+), 3 deletions(-) > > >> > > > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > >> > index 764db86..95594c3 100644 > > >> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > >> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > >> > @@ -17,6 +17,10 @@ Optional properties: > > >> > "pwms" property (see PWM binding[0]) > > >> > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > > >> > and disables the backlight (see GPIO binding[1]) > > >> > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > > >> > + and switching PWM on. This may be required to eliminate > > >> > + flicker when switching the PWM on after it has been > > >> > + disabled. > > >> > > >> The subject talks about turning on the backlight regulator, but this > > >> only talks about the PWM. > > > > > > From my understanding "switching PWM on" == enabling the regulator. > > > > > > I don't see any disparity here. Or am I missing something? > > > > The delay is from (re-)enabling the PWM (turning it on) to switching > > backlight power on. That sounds like 2 different things to me. I read it as the delay being between "configuring the PWM" (still not on) and "switching <the> PWM on" (enabling the regulator). > The text should better read: > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > + and switching the backlight regulator on. This may be > + required to eliminate flicker when switching the backlight > + on after it had been disabled. How is the regulator described in the datasheet? Is it for the Backlight or the PWM?
Hi, On Wed, 8 Nov 2017 09:12:12 +0000 Lee Jones wrote: > On Wed, 08 Nov 2017, Lothar Waßmann wrote: > > > Hi, > > > > On Tue, 7 Nov 2017 18:46:18 -0600 Rob Herring wrote: > > > On Mon, Oct 30, 2017 at 5:33 AM, Lee Jones <lee.jones@linaro.org> wrote: > > > > On Fri, 27 Oct 2017, Rob Herring wrote: > > > > > > > >> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > > > >> > When switching the backlight on, the LCD may need some time to adjust > > > >> > to the configured PWM duty cycle. Add a configurable delay between > > > >> > configuring the PWM and enabling the backlight regulator to account > > > >> > for this. > > > >> > > > > >> > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> > > > >> > --- > > > >> > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > > > >> > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > > > >> > 2 files changed, 23 insertions(+), 3 deletions(-) > > > >> > > > > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > > >> > index 764db86..95594c3 100644 > > > >> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > > >> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > > >> > @@ -17,6 +17,10 @@ Optional properties: > > > >> > "pwms" property (see PWM binding[0]) > > > >> > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > > > >> > and disables the backlight (see GPIO binding[1]) > > > >> > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > > > >> > + and switching PWM on. This may be required to eliminate > > > >> > + flicker when switching the PWM on after it has been > > > >> > + disabled. > > > >> > > > >> The subject talks about turning on the backlight regulator, but this > > > >> only talks about the PWM. > > > > > > > > From my understanding "switching PWM on" == enabling the regulator. > > > > > > > > I don't see any disparity here. Or am I missing something? > > > > > > The delay is from (re-)enabling the PWM (turning it on) to switching > > > backlight power on. That sounds like 2 different things to me. > > I read it as the delay being between "configuring the PWM" (still not > on) and "switching <the> PWM on" (enabling the regulator). > > > The text should better read: > > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > > + and switching the backlight regulator on. This may be > > + required to eliminate flicker when switching the backlight > > + on after it had been disabled. > > How is the regulator described in the datasheet? > > Is it for the Backlight or the PWM? > It actually is a Power Control input of the LCD panel, that is modeled as a fiexd-regulator in Linux. Lothar Waßmann -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt index 764db86..95594c3 100644 --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt @@ -17,6 +17,10 @@ Optional properties: "pwms" property (see PWM binding[0]) - enable-gpios: contains a single GPIO specifier for the GPIO which enables and disables the backlight (see GPIO binding[1]) + - turn-on-delay-ms: delay in milliseconds between configuring the PWM + and switching PWM on. This may be required to eliminate + flicker when switching the PWM on after it has been + disabled. [0]: Documentation/devicetree/bindings/pwm/pwm.txt [1]: Documentation/devicetree/bindings/gpio/gpio.txt diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 921f322..9578f65 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -23,6 +23,7 @@ #include <linux/pwm_backlight.h> #include <linux/regulator/consumer.h> #include <linux/slab.h> +#include <linux/delay.h> struct pwm_bl_data { struct pwm_device *pwm; @@ -35,6 +36,7 @@ struct pwm_bl_data { struct gpio_desc *enable_gpio; unsigned int scale; bool legacy; + int turn_on_delay_ms; int (*notify)(struct device *, int brightness); void (*notify_after)(struct device *, @@ -52,6 +54,17 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness) pwm_enable(pb->pwm); + if (pb->turn_on_delay_ms > 0) { + dev_dbg(pb->dev, "Sleeping %u..%uµs\n", + pb->turn_on_delay_ms * 1000, + pb->turn_on_delay_ms * 1100); + if (pb->turn_on_delay_ms > 20) + msleep(pb->turn_on_delay_ms); + else + usleep_range(pb->turn_on_delay_ms * 1000, + pb->turn_on_delay_ms * 1100); + } + err = regulator_enable(pb->power_supply); if (err < 0) dev_err(pb->dev, "failed to enable power supply\n"); @@ -108,8 +121,9 @@ static int pwm_backlight_update_status(struct backlight_device *bl) duty_cycle = compute_duty_cycle(pb, brightness); pwm_config(pb->pwm, duty_cycle, pb->period); pwm_backlight_power_on(pb, brightness); - } else + } else { pwm_backlight_power_off(pb); + } if (pb->notify_after) pb->notify_after(pb->dev, brightness); @@ -264,9 +278,9 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->scale = data->levels[i]; pb->levels = data->levels; - } else + } else { pb->scale = data->max_brightness; - + } pb->notify = data->notify; pb->notify_after = data->notify_after; pb->check_fb = data->check_fb; @@ -329,6 +343,8 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } + of_property_read_u32(node, "turn-on-delay-ms", &pb->turn_on_delay_ms); + dev_dbg(&pdev->dev, "got pwm for backlight\n"); /*
When switching the backlight on, the LCD may need some time to adjust to the configured PWM duty cycle. Add a configurable delay between configuring the PWM and enabling the backlight regulator to account for this. Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de> --- .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- 2 files changed, 23 insertions(+), 3 deletions(-)