linux-fbdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [v7 0/5] drm: Support basic DPCD backlight in panel-simple and add a new panel ATNA33XC20
@ 2021-06-19 10:40 Rajeev Nandan
  2021-06-19 10:40 ` [v7 1/5] drm/panel: add basic DP AUX backlight support Rajeev Nandan
  2021-06-19 10:40 ` [v7 2/5] drm/panel-simple: Support DP AUX backlight Rajeev Nandan
  0 siblings, 2 replies; 6+ messages in thread
From: Rajeev Nandan @ 2021-06-19 10:40 UTC (permalink / raw)
  To: dri-devel, linux-arm-msm, freedreno, devicetree
  Cc: Rajeev Nandan, linux-kernel, thierry.reding, sam, robdclark,
	dianders, lyude, jani.nikula, robh, laurent.pinchart, a.hajda,
	daniel.thompson, hoegsberg, abhinavk, seanpaul, kalyan_t,
	mkrishn, lee.jones, jingoohan1, linux-fbdev

This series adds the support for the eDP panel that needs the backlight
controlling over the DP AUX channel using DPCD registers of the panel
as per the VESA's standard.

This series also adds support for the Samsung eDP AMOLED panel that
needs DP AUX to control the backlight, and introduces new delays in the
@panel_desc.delay to support this panel.

This patch series depends on the following two series:
- Doug's series [1], exposed the DP AUX channel to the panel-simple.
- Lyude's series [2], introduced new drm helper functions for DPCD
  backlight.

This series is the logical successor to the series [3].

Changes in v1:
- Created dpcd backlight helper with very basic functionality, added
  backlight registration in the ti-sn65dsi86 bridge driver.

Changes in v2:
- Created a new DisplayPort aux backlight driver and moved the code from
  drm_dp_aux_backlight.c (v1) to the new driver.

Changes in v3:
- Fixed module compilation (kernel test bot).

Changes in v4:
- Added basic DPCD backlight support in panel-simple.
- Added support for a new Samsung panel ATNA33XC20 that needs DPCD
  backlight controlling and has a requirement of delays between enable
  GPIO and regulator.

Changes in v5:
Addressed review suggestions from Douglas:
- Created a new API drm_panel_dp_aux_backlight() in drm_panel.c
- Moved DP AUX backlight functions from panel-simple.c to drm_panel.c
- panel-simple probe() calls drm_panel_dp_aux_backlight() to create
  backlight when the backlight phandle is not specified in panel DT
  and DP AUX channel is present.
- Added check for drm_edp_backlight_supported() before registering.
- Removed the @uses_dpcd_backlight flag from panel_desc as this
  should be auto-detected.
- Updated comments/descriptions.

Changes in v6:
- Rebased
- Updated wanrning messages, fixed word wrapping in comments.
- Fixed ordering of memory allocation

Changes in v7:
- Updated the disable_to_power_off and power_to_enable panel delays
as discovered at <https://crrev.com/c/2966167> (Douglas)

[1] https://lore.kernel.org/dri-devel/20210525000159.3384921-1-dianders@chromium.org/
[2] https://lore.kernel.org/dri-devel/20210514181504.565252-1-lyude@redhat.com/
[3] https://lore.kernel.org/dri-devel/1619416756-3533-1-git-send-email-rajeevny@codeaurora.org/

Rajeev Nandan (5):
  drm/panel: add basic DP AUX backlight support
  drm/panel-simple: Support DP AUX backlight
  drm/panel-simple: Support for delays between GPIO & regulator
  dt-bindings: display: simple: Add Samsung ATNA33XC20
  drm/panel-simple: Add Samsung ATNA33XC20

 .../bindings/display/panel/panel-simple.yaml       |   2 +
 drivers/gpu/drm/drm_panel.c                        | 108 +++++++++++++++++++++
 drivers/gpu/drm/panel/panel-simple.c               |  67 +++++++++++++
 include/drm/drm_panel.h                            |  15 ++-
 4 files changed, 188 insertions(+), 4 deletions(-)

-- 
2.7.4


^ permalink raw reply	[flat|nested] 6+ messages in thread

* [v7 1/5] drm/panel: add basic DP AUX backlight support
  2021-06-19 10:40 [v7 0/5] drm: Support basic DPCD backlight in panel-simple and add a new panel ATNA33XC20 Rajeev Nandan
@ 2021-06-19 10:40 ` Rajeev Nandan
       [not found]   ` <20210620093141.GA703072@ravnborg.org>
  2021-06-19 10:40 ` [v7 2/5] drm/panel-simple: Support DP AUX backlight Rajeev Nandan
  1 sibling, 1 reply; 6+ messages in thread
From: Rajeev Nandan @ 2021-06-19 10:40 UTC (permalink / raw)
  To: dri-devel, linux-arm-msm, freedreno, devicetree
  Cc: Rajeev Nandan, linux-kernel, thierry.reding, sam, robdclark,
	dianders, lyude, jani.nikula, robh, laurent.pinchart, a.hajda,
	daniel.thompson, hoegsberg, abhinavk, seanpaul, kalyan_t,
	mkrishn, lee.jones, jingoohan1, linux-fbdev

Some panels support backlight control over DP AUX channel using
VESA's standard backlight control interface.
Using new DRM eDP backlight helpers, add support to create and
register a backlight for those panels in drm_panel to simplify
the panel drivers.

The panel driver with access to "struct drm_dp_aux" can create and
register a backlight device using following code snippet in its
probe() function:

	err = drm_panel_dp_aux_backlight(panel, aux);
	if (err)
		return err;

Then drm_panel will handle backlight_(enable|disable) calls
similar to the case when drm_panel_of_backlight() is used.

Currently, we are not supporting one feature where the source
device can combine the backlight brightness levels set through
DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
required for the basic backlight controls, it can be added later.

Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
---

(no changes since v6)

Changes in v5:
- New

Changes in v6:
- Fixed ordering of memory allocation (Douglas)
- Updated word wrapping in a comment (Douglas)

 drivers/gpu/drm/drm_panel.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_panel.h     |  15 ++++--
 2 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f634371..9e65342 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -26,12 +26,20 @@
 #include <linux/module.h>
 
 #include <drm/drm_crtc.h>
+#include <drm/drm_dp_helper.h>
 #include <drm/drm_panel.h>
 #include <drm/drm_print.h>
 
 static DEFINE_MUTEX(panel_lock);
 static LIST_HEAD(panel_list);
 
+struct dp_aux_backlight {
+	struct backlight_device *base;
+	struct drm_dp_aux *aux;
+	struct drm_edp_backlight_info info;
+	bool enabled;
+};
+
 /**
  * DOC: drm panel
  *
@@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel *panel)
 	return 0;
 }
 EXPORT_SYMBOL(drm_panel_of_backlight);
+
+static int dp_aux_backlight_update_status(struct backlight_device *bd)
+{
+	struct dp_aux_backlight *bl = bl_get_data(bd);
+	u16 brightness = backlight_get_brightness(bd);
+	int ret = 0;
+
+	if (brightness > 0) {
+		if (!bl->enabled) {
+			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
+			bl->enabled = true;
+			return 0;
+		}
+		ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
+	} else {
+		if (bl->enabled) {
+			drm_edp_backlight_disable(bl->aux, &bl->info);
+			bl->enabled = false;
+		}
+	}
+
+	return ret;
+}
+
+static const struct backlight_ops dp_aux_bl_ops = {
+	.update_status = dp_aux_backlight_update_status,
+};
+
+/**
+ * drm_panel_dp_aux_backlight - create and use DP AUX backlight
+ * @panel: DRM panel
+ * @aux: The DP AUX channel to use
+ *
+ * Use this function to create and handle backlight if your panel
+ * supports backlight control over DP AUX channel using DPCD
+ * registers as per VESA's standard backlight control interface.
+ *
+ * When the panel is enabled backlight will be enabled after a
+ * successful call to &drm_panel_funcs.enable()
+ *
+ * When the panel is disabled backlight will be disabled before the
+ * call to &drm_panel_funcs.disable().
+ *
+ * A typical implementation for a panel driver supporting backlight
+ * control over DP AUX will call this function at probe time.
+ * Backlight will then be handled transparently without requiring
+ * any intervention from the driver.
+ *
+ * drm_panel_dp_aux_backlight() must be called after the call to drm_panel_init().
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
+{
+	struct dp_aux_backlight *bl;
+	struct backlight_properties props = { 0 };
+	u16 current_level;
+	u8 current_mode;
+	u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
+	int ret;
+
+	if (!panel || !panel->dev || !aux)
+		return -EINVAL;
+
+	ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
+			       EDP_DISPLAY_CTL_CAP_SIZE);
+	if (ret < 0)
+		return ret;
+
+	if (!drm_edp_backlight_supported(edp_dpcd)) {
+		DRM_DEV_INFO(panel->dev, "DP AUX backlight is not supported\n");
+		return 0;
+	}
+
+	bl = devm_kzalloc(panel->dev, sizeof(*bl), GFP_KERNEL);
+	if (!bl)
+		return -ENOMEM;
+
+	bl->aux = aux;
+
+	ret = drm_edp_backlight_init(aux, &bl->info, 0, edp_dpcd,
+				     &current_level, &current_mode);
+	if (ret < 0)
+		return ret;
+
+	props.type = BACKLIGHT_RAW;
+	props.brightness = current_level;
+	props.max_brightness = bl->info.max;
+
+	bl->base = devm_backlight_device_register(panel->dev, "dp_aux_backlight",
+						  panel->dev, bl,
+						  &dp_aux_bl_ops, &props);
+	if (IS_ERR(bl->base))
+		return PTR_ERR(bl->base);
+
+	panel->backlight = bl->base;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
 #endif
 
 MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 33605c3..3ebfaa6 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -32,6 +32,7 @@ struct backlight_device;
 struct device_node;
 struct drm_connector;
 struct drm_device;
+struct drm_dp_aux;
 struct drm_panel;
 struct display_timing;
 
@@ -64,8 +65,8 @@ enum drm_panel_orientation;
  * the panel. This is the job of the .unprepare() function.
  *
  * Backlight can be handled automatically if configured using
- * drm_panel_of_backlight(). Then the driver does not need to implement the
- * functionality to enable/disable backlight.
+ * drm_panel_of_backlight() or drm_panel_dp_aux_backlight(). Then the driver
+ * does not need to implement the functionality to enable/disable backlight.
  */
 struct drm_panel_funcs {
 	/**
@@ -144,8 +145,8 @@ struct drm_panel {
 	 * Backlight device, used to turn on backlight after the call
 	 * to enable(), and to turn off backlight before the call to
 	 * disable().
-	 * backlight is set by drm_panel_of_backlight() and drivers
-	 * shall not assign it.
+	 * backlight is set by drm_panel_of_backlight() or
+	 * drm_panel_dp_aux_backlight() and drivers shall not assign it.
 	 */
 	struct backlight_device *backlight;
 
@@ -208,11 +209,17 @@ static inline int of_drm_get_panel_orientation(const struct device_node *np,
 #if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
 	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
 int drm_panel_of_backlight(struct drm_panel *panel);
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux);
 #else
 static inline int drm_panel_of_backlight(struct drm_panel *panel)
 {
 	return 0;
 }
+static inline int drm_panel_dp_aux_backlight(struct drm_panel *panel,
+					     struct drm_dp_aux *aux)
+{
+	return 0;
+}
 #endif
 
 #endif
-- 
2.7.4


^ permalink raw reply	[flat|nested] 6+ messages in thread

* [v7 2/5] drm/panel-simple: Support DP AUX backlight
  2021-06-19 10:40 [v7 0/5] drm: Support basic DPCD backlight in panel-simple and add a new panel ATNA33XC20 Rajeev Nandan
  2021-06-19 10:40 ` [v7 1/5] drm/panel: add basic DP AUX backlight support Rajeev Nandan
@ 2021-06-19 10:40 ` Rajeev Nandan
  1 sibling, 0 replies; 6+ messages in thread
From: Rajeev Nandan @ 2021-06-19 10:40 UTC (permalink / raw)
  To: dri-devel, linux-arm-msm, freedreno, devicetree
  Cc: Rajeev Nandan, linux-kernel, thierry.reding, sam, robdclark,
	dianders, lyude, jani.nikula, robh, laurent.pinchart, a.hajda,
	daniel.thompson, hoegsberg, abhinavk, seanpaul, kalyan_t,
	mkrishn, lee.jones, jingoohan1, linux-fbdev

If there is no backlight specified in the device tree and the panel
has access to the DP AUX channel then create a DP AUX backlight if
supported by the panel.

Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---

(no changes since v5)

This patch depends on the previous patch (2/5) of this series.

Changes in v4:
- New

Changes in v5:
- Address review comments and move backlight functions to drm_panel.c (Douglas)
- Create and register DP AUX backlight if there is no backlight specified in the
  device tree and panel has the DP AUX channel. (Douglas)
- The new drm_panel_dp_aux_backlight() will do the drm_edp_backlight_supported() check.

 drivers/gpu/drm/panel/panel-simple.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index df6fbd1..26555ec 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -800,6 +800,12 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc,
 	if (err)
 		goto disable_pm_runtime;
 
+	if (!panel->base.backlight && panel->aux) {
+		err = drm_panel_dp_aux_backlight(&panel->base, panel->aux);
+		if (err)
+			goto disable_pm_runtime;
+	}
+
 	drm_panel_add(&panel->base);
 
 	return 0;
-- 
2.7.4


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [v7 1/5] drm/panel: add basic DP AUX backlight support
       [not found]   ` <20210620093141.GA703072@ravnborg.org>
@ 2021-06-21  8:38     ` rajeevny
       [not found]       ` <20210621183828.GA918146@ravnborg.org>
  0 siblings, 1 reply; 6+ messages in thread
From: rajeevny @ 2021-06-21  8:38 UTC (permalink / raw)
  To: Sam Ravnborg
  Cc: dri-devel, linux-arm-msm, freedreno, devicetree, linux-kernel,
	thierry.reding, robdclark, dianders, lyude, jani.nikula, robh,
	laurent.pinchart, a.hajda, daniel.thompson, hoegsberg, abhinavk,
	seanpaul, kalyan_t, mkrishn, lee.jones, jingoohan1, linux-fbdev

Hi Sam,

On 20-06-2021 15:01, Sam Ravnborg wrote:
> Hi Rajeev
> 
> On Sat, Jun 19, 2021 at 04:10:26PM +0530, Rajeev Nandan wrote:
>> Some panels support backlight control over DP AUX channel using
>> VESA's standard backlight control interface.
>> Using new DRM eDP backlight helpers, add support to create and
>> register a backlight for those panels in drm_panel to simplify
>> the panel drivers.
>> 
>> The panel driver with access to "struct drm_dp_aux" can create and
>> register a backlight device using following code snippet in its
>> probe() function:
>> 
>> 	err = drm_panel_dp_aux_backlight(panel, aux);
>> 	if (err)
>> 		return err;
> 
> IT very good to have this supported by drm_panel, so we avoid
> bolierplate in various drivers.
> 
>> 
>> Then drm_panel will handle backlight_(enable|disable) calls
>> similar to the case when drm_panel_of_backlight() is used.
>> 
>> Currently, we are not supporting one feature where the source
>> device can combine the backlight brightness levels set through
>> DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
>> required for the basic backlight controls, it can be added later.
>> 
>> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
>> Reviewed-by: Douglas Anderson <dianders@chromium.org>
>> Reviewed-by: Lyude Paul <lyude@redhat.com>
>> ---
>> 
>> (no changes since v6)
>> 
>> Changes in v5:
>> - New
>> 
>> Changes in v6:
>> - Fixed ordering of memory allocation (Douglas)
>> - Updated word wrapping in a comment (Douglas)
>> 
>>  drivers/gpu/drm/drm_panel.c | 108 
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  include/drm/drm_panel.h     |  15 ++++--
>>  2 files changed, 119 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
>> index f634371..9e65342 100644
>> --- a/drivers/gpu/drm/drm_panel.c
>> +++ b/drivers/gpu/drm/drm_panel.c
>> @@ -26,12 +26,20 @@
>>  #include <linux/module.h>
>> 
>>  #include <drm/drm_crtc.h>
>> +#include <drm/drm_dp_helper.h>
>>  #include <drm/drm_panel.h>
>>  #include <drm/drm_print.h>
>> 
>>  static DEFINE_MUTEX(panel_lock);
>>  static LIST_HEAD(panel_list);
>> 
>> +struct dp_aux_backlight {
>> +	struct backlight_device *base;
>> +	struct drm_dp_aux *aux;
>> +	struct drm_edp_backlight_info info;
>> +	bool enabled;
>> +};
>> +
>>  /**
>>   * DOC: drm panel
>>   *
>> @@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel 
>> *panel)
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL(drm_panel_of_backlight);
>> +
>> +static int dp_aux_backlight_update_status(struct backlight_device 
>> *bd)
>> +{
>> +	struct dp_aux_backlight *bl = bl_get_data(bd);
>> +	u16 brightness = backlight_get_brightness(bd);
> backlight_get_brightness() returns an int, so using u16 seems wrong.
> But then drm_edp_backlight_enable() uses u16 for level - so I guess it
> is OK.
> We use unsigned long, int, u16 for brightness. Looks like something one
> could look at one day, but today is not that day.
> 
>> +	int ret = 0;
>> +
>> +	if (brightness > 0) {
> Use backlight_is_blank(bd) here, as this is really what you test for.

The backlight_get_brightness() used above has the backlight_is_blank() 
check and returns brightness 0 when the backlight_is_blank(bd) is true.
So, instead of calling backlight_is_blank(bd), we are checking 
brightness value here.
I took the reference from pwm_backlight_update_status() of the PWM 
backlight driver (drivers/video/backlight/pwm_bl.c)

Yes, we can change this _if_ condition to use backlight_is_blank(bd), as 
this is an inline function, and is more meaningful.
With this, there would be one change in the behavior of 
_backlight_update_status function in the following case:

- Setting brightness=0 when the backlight is not blank:
In the current case setting brightness=0 is disabling the backlight.
In the new case, setting brightness=0 will set the brightness to 0 and 
will do nothing to backlight disable.

I think that should not be a problem?

> 
> I cannot see why you need the extra check on ->enabled?
> Would it be sufficient to check backlight_is_blank() only?

This extra check on bl->enabled flag is added to avoid 
enabling/disabling backlight again if it is already enabled/disabled.
Using this flag way can know the transition between backlight blank and 
un-blank, and decide when to enable/disable the backlight.

> 
>> +		if (!bl->enabled) {
>> +			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
>> +			bl->enabled = true;
>> +			return 0;
>> +		}
>> +		ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
>> +	} else {
>> +		if (bl->enabled) {
>> +			drm_edp_backlight_disable(bl->aux, &bl->info);
>> +			bl->enabled = false;
>> +		}
>> +	}
>> +
>> +	return ret;
>> +}
> 
> 	Sam

Thanks,
Rajeev

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [v7 1/5] drm/panel: add basic DP AUX backlight support
       [not found]       ` <20210621183828.GA918146@ravnborg.org>
@ 2021-06-22 18:33         ` Doug Anderson
  2021-06-23  6:15           ` rajeevny
  0 siblings, 1 reply; 6+ messages in thread
From: Doug Anderson @ 2021-06-22 18:33 UTC (permalink / raw)
  To: Sam Ravnborg
  Cc: Rajeev Nandan, dri-devel, linux-arm-msm, freedreno,
	open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS, LKML,
	Thierry Reding, Rob Clark, Lyude Paul, Jani Nikula, Rob Herring,
	Laurent Pinchart, Andrzej Hajda, Daniel Thompson,
	Kristian H. Kristensen, Abhinav Kumar, Sean Paul, Kalyan Thota,
	Krishna Manikandan, Lee Jones, Jingoo Han, linux-fbdev

Hi,

On Mon, Jun 21, 2021 at 11:38 AM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> > > I cannot see why you need the extra check on ->enabled?
> > > Would it be sufficient to check backlight_is_blank() only?
> >
> > This extra check on bl->enabled flag is added to avoid enabling/disabling
> > backlight again if it is already enabled/disabled.
> > Using this flag way can know the transition between backlight blank and
> > un-blank, and decide when to enable/disable the backlight.
>
> My point is that this should really not be needed, as it would cover up
> for some other bug whaere we try to do something twice that is not
> needed. But I am less certain here so if you think it is needed, keep
> it as is.

I haven't tested this myself, but I believe that it is needed. I don't
think the backlight update_status() function is like an enable/disable
function. I believe it can be called more than one time even while the
backlight is disabled. For instance, you can see that
backlight_update_status() just blindly calls through to update the
status. That function can be called for a number of reasons. Perhaps
Rajeev can put some printouts to confirm but I think that if the
backlight is "blanked" for whatever reason and you write to sysfs and
change the backlight level you'll still get called again even though
the backlight is still "disabled".

-Doug

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [v7 1/5] drm/panel: add basic DP AUX backlight support
  2021-06-22 18:33         ` Doug Anderson
@ 2021-06-23  6:15           ` rajeevny
  0 siblings, 0 replies; 6+ messages in thread
From: rajeevny @ 2021-06-23  6:15 UTC (permalink / raw)
  To: Doug Anderson
  Cc: Sam Ravnborg, dri-devel, linux-arm-msm, freedreno,
	open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS, LKML,
	Thierry Reding, Rob Clark, Lyude Paul, Jani Nikula, Rob Herring,
	Laurent Pinchart, Andrzej Hajda, Daniel Thompson,
	Kristian H. Kristensen, Abhinav Kumar, Sean Paul, Kalyan Thota,
	Krishna Manikandan, Lee Jones, Jingoo Han, linux-fbdev

Hi,

On 23-06-2021 00:03, Doug Anderson wrote:
> Hi,
> 
> On Mon, Jun 21, 2021 at 11:38 AM Sam Ravnborg <sam@ravnborg.org> wrote:
>> 
>> > > I cannot see why you need the extra check on ->enabled?
>> > > Would it be sufficient to check backlight_is_blank() only?
>> >
>> > This extra check on bl->enabled flag is added to avoid enabling/disabling
>> > backlight again if it is already enabled/disabled.
>> > Using this flag way can know the transition between backlight blank and
>> > un-blank, and decide when to enable/disable the backlight.
>> 
>> My point is that this should really not be needed, as it would cover 
>> up
>> for some other bug whaere we try to do something twice that is not
>> needed. But I am less certain here so if you think it is needed, keep
>> it as is.
> 
> I haven't tested this myself, but I believe that it is needed. I don't
> think the backlight update_status() function is like an enable/disable
> function. I believe it can be called more than one time even while the
> backlight is disabled. For instance, you can see that
> backlight_update_status() just blindly calls through to update the
> status. That function can be called for a number of reasons. Perhaps
> Rajeev can put some printouts to confirm but I think that if the
> backlight is "blanked" for whatever reason and you write to sysfs and
> change the backlight level you'll still get called again even though
> the backlight is still "disabled".
> 
Yes, sysfs write will always try to update the backlight even though the 
backlight is "blanked".

The "bl->enabled" check is also required to prevent unnecessary calls to 
drm_edp_backlight_enable() during every backlight level change.

To confirm this, I have added few prints in 
dp_aux_backlight_update_status() function and collected the logs.
(Copying the code here to make the review easy)


static int dp_aux_backlight_update_status(struct backlight_device *bd)
{
         struct dp_aux_backlight *bl = bl_get_data(bd);
         u16 brightness = backlight_get_brightness(bd);
         int ret = 0;

+        pr_err("%s: brightness %d, _is_blank %d, bl->enabled %d\n", 
__func__,
+                brightness, backlight_is_blank(bd), bl->enabled);

         if (!backlight_is_blank(bd)) {
                 if (!bl->enabled) {
+                        pr_err("%s: enabling backlight\n", __func__);
                         drm_edp_backlight_enable(bl->aux, &bl->info, 
brightness);
                         bl->enabled = true;
                         return 0;
                 }
                 ret = drm_edp_backlight_set_level(bl->aux, &bl->info, 
brightness);
         } else {
                 if (bl->enabled) {
+                       pr_err("%s: disabling backlight\n", __func__);
                         drm_edp_backlight_disable(bl->aux, &bl->info);
                         bl->enabled = false;
                 }
         }

         return ret;
}


LOGS
====

During boot
-----------
[    4.752188] dp_aux_backlight_update_status: brightness 102, _is_blank 
0, bl->enabled 0
[    4.760447] dp_aux_backlight_update_status: enabling backlight
[    5.503866] dp_aux_backlight_update_status: brightness 102, _is_blank 
0, bl->enabled 1
[    6.897355] dp_aux_backlight_update_status: brightness 103, _is_blank 
0, bl->enabled 1
[    6.938617] dp_aux_backlight_update_status: brightness 104, _is_blank 
0, bl->enabled 1
[    6.980634] dp_aux_backlight_update_status: brightness 105, _is_blank 
0, bl->enabled 1


Turning Panel OFF
-----------------
localhost ~ # set_power_policy --ac_screen_dim_delay=5 
--ac_screen_off_delay=10
localhost ~ #

[  106.555140] dp_aux_backlight_update_status: brightness 145, _is_blank 
0, bl->enabled 1
...
...
[  111.679407] dp_aux_backlight_update_status: brightness 7, _is_blank 
0, bl->enabled 1
[  111.700302] dp_aux_backlight_update_status: brightness 4, _is_blank 
0, bl->enabled 1
[  111.720805] dp_aux_backlight_update_status: brightness 2, _is_blank 
0, bl->enabled 1
[  111.747486] dp_aux_backlight_update_status: brightness 0, _is_blank 
1, bl->enabled 1
[  111.755580] dp_aux_backlight_update_status: disabling backlight
[  111.792344] dp_aux_backlight_update_status: brightness 0, _is_blank 
1, bl->enabled 0


Changing brightness from sysfs while panel is off
--------------------------------------------------
(it will do nothing)

localhost ~ # echo 100 > 
/sys/class/backlight/dp_aux_backlight/brightness
[  352.754963] dp_aux_backlight_update_status: brightness 0, _is_blank 
1, bl->enabled 0

localhost ~ # echo 200 > 
/sys/class/backlight/dp_aux_backlight/brightness
[  364.708048] dp_aux_backlight_update_status: brightness 0, _is_blank 
1, bl->enabled 0

localhost ~ # echo 0 > /sys/class/backlight/dp_aux_backlight/brightness
[  378.850978] dp_aux_backlight_update_status: brightness 0, _is_blank 
1, bl->enabled 0


Turning Panel ON
----------------
[  553.381745] dp_aux_backlight_update_status: brightness 0, _is_blank 
0, bl->enabled 0
[  553.418133] dp_aux_backlight_update_status: enabling backlight
[  553.426397] dp_aux_backlight_update_status: brightness 159, _is_blank 
0, bl->enabled 1

====



Thanks,
Rajeev


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-06-23  6:15 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-06-19 10:40 [v7 0/5] drm: Support basic DPCD backlight in panel-simple and add a new panel ATNA33XC20 Rajeev Nandan
2021-06-19 10:40 ` [v7 1/5] drm/panel: add basic DP AUX backlight support Rajeev Nandan
     [not found]   ` <20210620093141.GA703072@ravnborg.org>
2021-06-21  8:38     ` rajeevny
     [not found]       ` <20210621183828.GA918146@ravnborg.org>
2021-06-22 18:33         ` Doug Anderson
2021-06-23  6:15           ` rajeevny
2021-06-19 10:40 ` [v7 2/5] drm/panel-simple: Support DP AUX backlight Rajeev Nandan

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox