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- Fix interpolation issues by switching to a linear algorithm; pwm_bl
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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
This commit is contained in:
Linus Torvalds 2020-12-16 14:52:37 -08:00
commit 84e010ec8f
1 changed files with 30 additions and 38 deletions
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68
drivers/video/backlight/pwm_bl.c
View File

@ -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[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;
/* 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++;
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;