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

Enric Balletbo i Serra
2018-08-24T15:54:02Z

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(-)

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,
--
2.18.0