From: Enric Balletbo i Serra <hidden> Date: 2017-06-30 11:21:52
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds. [0]: Documentation/devicetree/bindings/pwm/pwm.txt [1]: Documentation/devicetree/bindings/gpio/gpio.txt
From: Enric Balletbo i Serra <hidden> Date: 2017-06-30 11:21:50
The minnie devices comes with an AUO B101EAN01 panel which is different
from default veyron devices, thus the power on/off timing sequence is
slightly different. The datasheet specifies a pwm delay of 200 ms, so
update the pwm-delay-us accordingly.
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Heiko,
I'm not able to test this patch in a minnie device because I don't have
one, so could you do a quick try, please?
Thanks,
Enric
Changes since v1:
- Add this new patch as minnie has differents timings.
arch/arm/boot/dts/rk3288-veyron-minnie.dts | 1 +
1 file changed, 1 insertion(+)
From: Enric Balletbo i Serra <hidden> Date: 2017-06-30 11:21:51
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);+if(pb->enable_gpio)gpiod_set_value_cansleep(pb->enable_gpio,1);-pwm_enable(pb->pwm);pb->enabled=true;}
@@ -13,6 +13,7 @@ struct platform_pwm_backlight_data {unsignedintlth_brightness;unsignedintpwm_period_ns;unsignedint*levels;+unsignedintpwm_delay[2];/* TODO remove once all users are switched to gpiod_* API */intenable_gpio;int(*init)(structdevice*dev);
From: Enric Balletbo i Serra <hidden> Date: 2017-06-30 11:21:51
For veyron the binding should provide both pwm timings, the delay between
you enable the PWM and set the enable signal, and the delay between you
disable the PWM signal and clear the enable signal. Update the binding
accordingly, in this case the panels connected to the veyron boards have
a symetric power sequence, hence the same value is used.
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- Add this new patch to fix current binding on veyron.
arch/arm/boot/dts/rk3288-veyron-chromebook.dtsi | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
From: Pavel Machek <hidden> Date: 2017-06-30 11:25:23
On Fri 2017-06-30 13:21:06, Enric Balletbo i Serra wrote:
quoted hunk
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.
"Hardware needs a delay between setting an initial (non-zero) PWM and
enabling the backlight using GPIO. The 1st cell specifies this delay
in micro seconds. Hardware also needs a delay between disabing the
backlight using GPIO and setting PWM value to 0. The 2nd cell is this
delay in micro seconds."
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Two more comments below.
quoted hunk
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);
2000 us is kind of arbitrary. What if pwm_delay[0] is on the order of 20
us? Making the delay 2 ms longer (in the worst case) seems somewhat
excessive. Why not something like:
usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] * 2);
?
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted hunk
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);+if(pb->enable_gpio)gpiod_set_value_cansleep(pb->enable_gpio,1);-pwm_enable(pb->pwm);pb->enabled=true;}
@@ -174,6 +183,12 @@ static int pwm_backlight_parse_dt(struct device *dev,data->max_brightness--;}+/* read pwm to enable pre/post delays from DT property */+ret=of_property_read_u32_array(node,"pwm-delay-us",data->pwm_delay,+ARRAY_SIZE(data->pwm_delay));+if(ret<0)+returnret;
Also I think you need to make sure you have a fallback in place in case
that this fails, otherwise the property is no longer optional.
Ignoring -EINVAL should do the trick since data->pwm_delay should be
zeroed out by the memset() earlier in this function.
Thierry
Hi Thierry,
Many thanks for your comments, I'll send a v3.
2017-07-06 10:13 GMT+02:00 Thierry Reding [off-list ref]:
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);+if(pb->enable_gpio)gpiod_set_value_cansleep(pb->enable_gpio,1);-pwm_enable(pb->pwm);pb->enabled=true;}
@@ -174,6 +183,12 @@ static int pwm_backlight_parse_dt(struct device *dev,data->max_brightness--;}+/* read pwm to enable pre/post delays from DT property */+ret=of_property_read_u32_array(node,"pwm-delay-us",data->pwm_delay,+ARRAY_SIZE(data->pwm_delay));+if(ret<0)+returnret;
Also I think you need to make sure you have a fallback in place in case
that this fails, otherwise the property is no longer optional.
Ignoring -EINVAL should do the trick since data->pwm_delay should be
zeroed out by the memset() earlier in this function.
From: Pavel Machek <hidden> Date: 2017-07-06 09:12:47
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Don't make this overly complex. This is trivial. No need to split it
into more patches.
Two more comments below.
quoted
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);
2000 us is kind of arbitrary. What if pwm_delay[0] is on the order of 20
us? Making the delay 2 ms longer (in the worst case) seems somewhat
excessive. Why not something like:
usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] * 2);
?
From: Daniel Thompson <hidden> Date: 2017-07-06 09:17:25
On 06/07/17 10:12, Pavel Machek wrote:
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
quoted
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Don't make this overly complex. This is trivial. No need to split it
into more patches.
Agree. IMHO getting the code that reads the (optional) new parameter
correct is the best way to manage risk of regression since in most cases
the delay will be skipped anyway.
Daniel.
quoted
Two more comments below.
quoted
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
- Move the check of dt property to the parse dt function.
v1: https://lkml.org/lkml/2017/6/28/219
drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
include/linux/pwm_backlight.h | 1 +
2 files changed, 21 insertions(+), 4 deletions(-)
@@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)if(err<0)dev_err(pb->dev,"failed to enable power supply\n");+pwm_enable(pb->pwm);++if(pb->pwm_delay[0])+usleep_range(pb->pwm_delay[0],pb->pwm_delay[0]+2000);
2000 us is kind of arbitrary. What if pwm_delay[0] is on the order of 20
us? Making the delay 2 ms longer (in the worst case) seems somewhat
excessive. Why not something like:
usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] * 2);
?
On Thu, Jul 06, 2017 at 10:17:18AM +0100, Daniel Thompson wrote:
On 06/07/17 10:12, Pavel Machek wrote:
quoted
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
quoted
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Don't make this overly complex. This is trivial. No need to split it
into more patches.
Agree. IMHO getting the code that reads the (optional) new parameter correct
is the best way to manage risk of regression since in most cases the delay
will be skipped anyway.
The potential regression that I'm referring to would be caused by
inversing the sequence (GPIO enable -> PWM enable). That's completely
unrelated to the delays introduced by this patch. Many boards use this
driver and they've been running with the old sequence for many years.
Granted, it's fairly unlikely to regress, but it's still a possibility.
Given that both changes are logically separate, I think separate patches
are totally appropriate. I also don't think that this would overly
complicate things.
Thierry
From: Pavel Machek <hidden> Date: 2017-07-06 09:55:06
Hi!
On Thu 2017-07-06 11:24:48, Thierry Reding wrote:
On Thu, Jul 06, 2017 at 10:17:18AM +0100, Daniel Thompson wrote:
quoted
On 06/07/17 10:12, Pavel Machek wrote:
quoted
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
quoted
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Don't make this overly complex. This is trivial. No need to split it
into more patches.
Agree. IMHO getting the code that reads the (optional) new parameter correct
is the best way to manage risk of regression since in most cases the delay
will be skipped anyway.
The potential regression that I'm referring to would be caused by
inversing the sequence (GPIO enable -> PWM enable). That's completely
unrelated to the delays introduced by this patch. Many boards use this
driver and they've been running with the old sequence for many years.
Granted, it's fairly unlikely to regress, but it's still a
possibility.
Given that both changes are logically separate, I think separate patches
are totally appropriate. I also don't think that this would overly
complicate things.
From: Daniel Thompson <hidden> Date: 2017-07-06 09:57:33
On 06/07/17 10:24, Thierry Reding wrote:
On Thu, Jul 06, 2017 at 10:17:18AM +0100, Daniel Thompson wrote:
quoted
On 06/07/17 10:12, Pavel Machek wrote:
quoted
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
quoted
On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
quoted
From: huang lin <redacted>
Some panels (i.e. N116BGE-L41), in their power sequence specifications,
request a delay between set the PWM signal and enable the backlight and
between clear the PWM signal and disable the backlight. Add support for
the new pwm-delay-us property to meet the timing.
Note that this patch inverts current sequence. Before this patch the
enable signal was set before the PWM signal and vice-versa on power off.
I assumed that this sequence was wrong, at least it is on different panel
datasheets that I checked, so I inverted the sequence to follow:
On power on, set the PWM signal, wait, and set the LED_EN signal.
On power off, clear the LED_EN signal, wait, and stop the PWM signal.
I think this should be two separate patches to make it easier to revert
the inverted sequence should it prove to regress on other panels.
Don't make this overly complex. This is trivial. No need to split it
into more patches.
Agree. IMHO getting the code that reads the (optional) new parameter correct
is the best way to manage risk of regression since in most cases the delay
will be skipped anyway.
The potential regression that I'm referring to would be caused by
inversing the sequence (GPIO enable -> PWM enable). That's completely
unrelated to the delays introduced by this patch. Many boards use this
driver and they've been running with the old sequence for many years.
Granted, it's fairly unlikely to regress, but it's still a possibility.
Given that both changes are logically separate, I think separate patches
are totally appropriate. I also don't think that this would overly
complicate things.
... and you are right on both counts!
Thanks for the detailed reply.
Daniel.
From: Rob Herring <robh+dt@kernel.org> Date: 2017-07-06 17:07:59
On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:
quoted hunk
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds.
pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.
I don't understand why you even need a post delay. The PWM can be set
to 0 while enabled, right? So if the PWM is set to 0 while enabled and
then disable the backlight, then there's no delay. Plus this doesn't
make much sense to me electrically either. The PWM duty cycle is going
to be completely async to the enable line change. The PWM state could
go from 1 to 0 at any point in time relative to the enable line
change.
These issues are the problem with generic bindings. Adding 1 property
is no big deal, but then what happens with the next variation. These
timing constraints need to be able to be implied by the panel's
compatible.
Rob
Hi Rob,
2017-07-06 19:07 GMT+02:00 Rob Herring [off-list ref]:
On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:
quoted
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds.
pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.
Maybe, Only I can say that the panels I checked always first enable
the PWM and then set the ENABLE signal, but of course I didn't check
all the panels.
Would be more acceptable have enable-delay-us and disable-delay-us proprieties?
I don't understand why you even need a post delay. The PWM can be set
to 0 while enabled, right? So if the PWM is set to 0 while enabled and
then disable the backlight, then there's no delay. Plus this doesn't
make much sense to me electrically either. The PWM duty cycle is going
to be completely async to the enable line change. The PWM state could
go from 1 to 0 at any point in time relative to the enable line
change.
To be honest I'm also not sure why is required the post delay, some
panels specify a 0 but others specifies a minimum value between you
off the panel and disable the PWM. The only reason I added the post
delay is because the different datasheets specifies it, I don't have a
use case that the post delay is used to fix something.
Thanks,
Enric
These issues are the problem with generic bindings. Adding 1 property
is no big deal, but then what happens with the next variation. These
timing constraints need to be able to be implied by the panel's
compatible.
Rob
Hi Rob,
2017-07-06 19:07 GMT+02:00 Rob Herring [off-list ref]:
quoted
On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:
quoted
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds.
pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.
A second proposal, what do you think?
- post-pwm-on-delay-us: Delay in us after setting an initial (non-zero) PWM
and enabling the backlight using GPIO.
- pwm-off-delay-us: Delay in us after disabling the backlight using a GPIO
and setting PWM value to 0.
Thanks,
Enric
Maybe, Only I can say that the panels I checked always first enable
the PWM and then set the ENABLE signal, but of course I didn't check
all the panels.
Would be more acceptable have enable-delay-us and disable-delay-us proprieties?
quoted
I don't understand why you even need a post delay. The PWM can be set
to 0 while enabled, right? So if the PWM is set to 0 while enabled and
then disable the backlight, then there's no delay. Plus this doesn't
make much sense to me electrically either. The PWM duty cycle is going
to be completely async to the enable line change. The PWM state could
go from 1 to 0 at any point in time relative to the enable line
change.
To be honest I'm also not sure why is required the post delay, some
panels specify a 0 but others specifies a minimum value between you
off the panel and disable the PWM. The only reason I added the post
delay is because the different datasheets specifies it, I don't have a
use case that the post delay is used to fix something.
Thanks,
Enric
quoted
These issues are the problem with generic bindings. Adding 1 property
is no big deal, but then what happens with the next variation. These
timing constraints need to be able to be implied by the panel's
compatible.
Rob
Hi Rob,
2017-07-06 19:07 GMT+02:00 Rob Herring [off-list ref]:
quoted
On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:
quoted
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds.
pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.
A second proposal, what do you think?
- post-pwm-on-delay-us: Delay in us after setting an initial (non-zero) PWM
and enabling the backlight using GPIO.
Hi Rob,
2017-07-06 19:07 GMT+02:00 Rob Herring [off-list ref]:
quoted
On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:
quoted
From: huang lin <redacted>
Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.
Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
- As suggested by Daniel Thompson
- Do not assume power-on delay and power-off delay will be the same
v1: https://lkml.org/lkml/2017/6/28/219
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
1 file changed, 6 insertions(+)
@@ -17,6 +17,11 @@ 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])+ - pwm-delay-us: delay between setting an initial (non-zero) PWM value and+ enabling the backlight, and also the delay between disabling+ the backlight and setting PWM value to 0.+ The 1st cell is the pre-delay in micro seconds.+ The 2nd cell is the post-delay in micro seconds.
pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.
A second proposal, what do you think?
- post-pwm-on-delay-us: Delay in us after setting an initial (non-zero) PWM
and enabling the backlight using GPIO.
This says "PWM on", "enable GPIO", "delay". Which is not what you
want.
Ok, seems I need to improve a bit more my English skills. :)
after -> between ?
Then, if I understand correctly, this (found in another binding that I
used as reference)
- post-power-on-delay-ms : Delay in ms after powering the card and
de-asserting the reset-gpios (if any)
means,
Power the card, de-asserting reset, delay ?
Regards,
Enric.