backlight: pwm_bl: Fix brightness levels for non-DT case.

Message ID 20180824155402.2822-1-enric.balletbo@collabora.com
State New
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Series
  • backlight: pwm_bl: Fix brightness levels for non-DT case.
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Commit Message

Enric Balletbo i Serra Aug. 24, 2018, 3:54 p.m.
Commit '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED
linearly to human eye")' allows the possibility to compute a default
brightness table when there isn't the brightness-levels property in the
DT. Unfortunately the changes made broke the pwm backlight for the
non-DT boards.

Usually, the non-DT boards don't pass the brightness levels via platform
data, instead, they set the max_brightness in their platform data and the
driver calculates the level without a table. The ofending patch assumed
that when there is no brightness levels table we should create one, but this
is clearly wrong for the non-DT case.

After this patch the code handles the DT and the non-DT case taking in
consideration also if max_brightness is set or not. The default table is
only created when neither, brightness-levels and max_brightness, are
set.

The patch also fixes another issue found by Robert. Before this patch
looks like a division by 0 was possible when state.period returned 0 by
pwm_get_state(). This is because pwm_get_state() was called before
pwm_apply_args() so state.period was not initialized. The patch moves
the pwm_apply_args() call before any call to pwm_get_state().

Fixes: '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")'
Reported-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
---

 drivers/video/backlight/pwm_bl.c | 50 ++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 12 deletions(-)

Comments

Robert Jarzmik Aug. 25, 2018, 8:04 a.m. | #1
Enric Balletbo i Serra <enric.balletbo@collabora.com> writes:

> Commit '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED
> linearly to human eye")' allows the possibility to compute a default
> brightness table when there isn't the brightness-levels property in the
> DT. Unfortunately the changes made broke the pwm backlight for the
> non-DT boards.
>
> Usually, the non-DT boards don't pass the brightness levels via platform
> data, instead, they set the max_brightness in their platform data and the
> driver calculates the level without a table. The ofending patch assumed
> that when there is no brightness levels table we should create one, but this
> is clearly wrong for the non-DT case.
>
> After this patch the code handles the DT and the non-DT case taking in
> consideration also if max_brightness is set or not. The default table is
> only created when neither, brightness-levels and max_brightness, are
> set.
>
> The patch also fixes another issue found by Robert. Before this patch
> looks like a division by 0 was possible when state.period returned 0 by
> pwm_get_state(). This is because pwm_get_state() was called before
> pwm_apply_args() so state.period was not initialized. The patch moves
> the pwm_apply_args() call before any call to pwm_get_state().
>
> Fixes: '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")'
> Reported-by: Robert Jarzmik <robert.jarzmik@free.fr>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>

Cheers.

--
Robert
Daniel Thompson Sept. 20, 2018, 4:23 p.m. | #2
On 25/08/18 01:04, Robert Jarzmik wrote:
> Enric Balletbo i Serra <enric.balletbo@collabora.com> writes:
> 
>> Commit '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED
>> linearly to human eye")' allows the possibility to compute a default
>> brightness table when there isn't the brightness-levels property in the
>> DT. Unfortunately the changes made broke the pwm backlight for the
>> non-DT boards.
>>
>> Usually, the non-DT boards don't pass the brightness levels via platform
>> data, instead, they set the max_brightness in their platform data and the
>> driver calculates the level without a table. The ofending patch assumed
>> that when there is no brightness levels table we should create one, but this
>> is clearly wrong for the non-DT case.
>>
>> After this patch the code handles the DT and the non-DT case taking in
>> consideration also if max_brightness is set or not. The default table is
>> only created when neither, brightness-levels and max_brightness, are
>> set.
>>
>> The patch also fixes another issue found by Robert. Before this patch
>> looks like a division by 0 was possible when state.period returned 0 by
>> pwm_get_state(). This is because pwm_get_state() was called before
>> pwm_apply_args() so state.period was not initialized. The patch moves
>> the pwm_apply_args() call before any call to pwm_get_state().
>>
>> Fixes: '88ba95bedb79 ("backlight: pwm_bl: Compute brightness of LED linearly to human eye")'
>> Reported-by: Robert Jarzmik <robert.jarzmik@free.fr>
>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

(and sorry for the delay)


Daniel.

Patch

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index bdfcc0a71db1..19770f7bffe4 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -539,7 +539,33 @@  static int pwm_backlight_probe(struct platform_device *pdev)
 
 	dev_dbg(&pdev->dev, "got pwm for backlight\n");
 
-	if (!data->levels) {
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(pb->pwm);
+
+	if (data->levels) {
+		/*
+		 * For the DT case, only when brightness levels is defined
+		 * data->levels is filled. For the non-DT case, data->levels
+		 * can come from platform data, however is not usual.
+		 */
+		for (i = 0; i <= data->max_brightness; i++) {
+			if (data->levels[i] > pb->scale)
+				pb->scale = data->levels[i];
+
+			pb->levels = data->levels;
+		}
+	} else if (!data->max_brightness) {
+		/*
+		 * If no brightness levels are provided and max_brightness is
+		 * not set, use the default brightness table. For the DT case,
+		 * max_brightness is set to 0 when brightness levels is not
+		 * specified. For the non-DT case, max_brightness is usually
+		 * set to some value.
+		 */
+
 		/* Get the PWM period (in nanoseconds) */
 		pwm_get_state(pb->pwm, &state);
 
@@ -550,21 +576,21 @@  static int pwm_backlight_probe(struct platform_device *pdev)
 				"failed to setup default brightness table\n");
 			goto err_alloc;
 		}
-	}
 
-	for (i = 0; i <= data->max_brightness; i++) {
-		if (data->levels[i] > pb->scale)
-			pb->scale = data->levels[i];
+		for (i = 0; i <= data->max_brightness; i++) {
+			if (data->levels[i] > pb->scale)
+				pb->scale = data->levels[i];
 
-		pb->levels = data->levels;
+			pb->levels = data->levels;
+		}
+	} else {
+		/*
+		 * That only happens for the non-DT case, where platform data
+		 * sets the max_brightness value.
+		 */
+		pb->scale = data->max_brightness;
 	}
 
-	/*
-	 * FIXME: pwm_apply_args() should be removed when switching to
-	 * the atomic PWM API.
-	 */
-	pwm_apply_args(pb->pwm);
-
 	/*
 	 * The DT case will set the pwm_period_ns field to 0 and store the
 	 * period, parsed from the DT, in the PWM device. For the non-DT case,