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authorLinus Torvalds <torvalds@linux-foundation.org>2020-12-16 14:52:37 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-12-16 14:52:37 -0800
commit84e010ec8f8668c579b78a27b0e81a49ac6c837a (patch)
tree559b47dcc507060014c356339f6bd37bc8923727 /drivers
parent278f54c46164e9859090dde7e4ceede830c6beb6 (diff)
parent789eb04b6c569e3e5007afd040bef5d7216d2f3a (diff)
Merge tag 'backlight-next-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight
Pull backlight update from Lee Jones: "Careful, it's a big one! - Fix pwm_bl driver interpolation issues by switching to a linear algorithm" * tag 'backlight-next-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight: backlight: pwm_bl: Fix interpolation
Diffstat (limited to 'drivers')
-rw-r--r--drivers/video/backlight/pwm_bl.c70
1 files changed, 31 insertions, 39 deletions
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index dfc760830eb9..e48fded3e414 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -230,8 +230,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
struct platform_pwm_backlight_data *data)
{
struct device_node *node = dev->of_node;
- unsigned int num_levels = 0;
- unsigned int levels_count;
+ unsigned int num_levels;
unsigned int num_steps = 0;
struct property *prop;
unsigned int *table;
@@ -260,12 +259,11 @@ static int pwm_backlight_parse_dt(struct device *dev,
if (!prop)
return 0;
- data->max_brightness = length / sizeof(u32);
+ num_levels = length / sizeof(u32);
/* read brightness levels from DT property */
- if (data->max_brightness > 0) {
- size_t size = sizeof(*data->levels) * data->max_brightness;
- unsigned int i, j, n = 0;
+ if (num_levels > 0) {
+ size_t size = sizeof(*data->levels) * num_levels;
data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
if (!data->levels)
@@ -273,7 +271,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
ret = of_property_read_u32_array(node, "brightness-levels",
data->levels,
- data->max_brightness);
+ num_levels);
if (ret < 0)
return ret;
@@ -298,7 +296,13 @@ static int pwm_backlight_parse_dt(struct device *dev,
* between two points.
*/
if (num_steps) {
- if (data->max_brightness < 2) {
+ unsigned int num_input_levels = num_levels;
+ unsigned int i;
+ u32 x1, x2, x, dx;
+ u32 y1, y2;
+ s64 dy;
+
+ if (num_input_levels < 2) {
dev_err(dev, "can't interpolate\n");
return -EINVAL;
}
@@ -308,14 +312,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
* taking in consideration the number of interpolated
* steps between two levels.
*/
- for (i = 0; i < data->max_brightness - 1; i++) {
- if ((data->levels[i + 1] - data->levels[i]) /
- num_steps)
- num_levels += num_steps;
- else
- num_levels++;
- }
- num_levels++;
+ num_levels = (num_input_levels - 1) * num_steps + 1;
dev_dbg(dev, "new number of brightness levels: %d\n",
num_levels);
@@ -327,24 +324,25 @@ static int pwm_backlight_parse_dt(struct device *dev,
table = devm_kzalloc(dev, size, GFP_KERNEL);
if (!table)
return -ENOMEM;
-
- /* Fill the interpolated table. */
- levels_count = 0;
- for (i = 0; i < data->max_brightness - 1; i++) {
- value = data->levels[i];
- n = (data->levels[i + 1] - value) / num_steps;
- if (n > 0) {
- for (j = 0; j < num_steps; j++) {
- table[levels_count] = value;
- value += n;
- levels_count++;
- }
- } else {
- table[levels_count] = data->levels[i];
- levels_count++;
+ /*
+ * Fill the interpolated table[x] = y
+ * by draw lines between each (x1, y1) to (x2, y2).
+ */
+ dx = num_steps;
+ for (i = 0; i < num_input_levels - 1; i++) {
+ x1 = i * dx;
+ x2 = x1 + dx;
+ y1 = data->levels[i];
+ y2 = data->levels[i + 1];
+ dy = (s64)y2 - y1;
+
+ for (x = x1; x < x2; x++) {
+ table[x] = y1 +
+ div_s64(dy * (x - x1), dx);
}
}
- table[levels_count] = data->levels[i];
+ /* Fill in the last point, since no line starts here. */
+ table[x2] = y2;
/*
* As we use interpolation lets remove current
@@ -353,15 +351,9 @@ static int pwm_backlight_parse_dt(struct device *dev,
*/
devm_kfree(dev, data->levels);
data->levels = table;
-
- /*
- * Reassign max_brightness value to the new total number
- * of brightness levels.
- */
- data->max_brightness = num_levels;
}
- data->max_brightness--;
+ data->max_brightness = num_levels - 1;
}
return 0;