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- Core Frameworks

Browse source 
- Remove unused/obsolete code/comments
 
  - New Functionality
    - Allow less granular brightness specification for high-res PWMs; pwm_bl
    - Align brightness {inc,dec}rements with that perceived by the human-eye; pwm_bl
 
  - Fix-ups
    - Prepare for the introduction of -Wimplicit-fall-through; adp8860_bl
 
  - Bug Fixes
    - Fix uninitialised variable; pwm_bl
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Merge tag 'backlight-next-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight

Pull backlight updates from Lee Jones:
 "Core Framework:
   - Remove unused/obsolete code/comments

  New Functionality:
   - Allow less granular brightness specification for high-res PWMs; pwm_bl
   - Align brightness {inc,dec}rements with that perceived by the human-eye; pwm_bl

  Fix-ups:
   - Prepare for the introduction of -Wimplicit-fall-through; adp8860_bl

  Bug Fixes:
   - Fix uninitialised variable; pwm_bl"

* tag 'backlight-next-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Fix uninitialized variable
  backlight: adp8860: Mark expected switch fall-through
  backlight: Remove obsolete comment for ->state
  dt-bindings: pwm-backlight: Move brightness-levels to optional
  backlight: pwm_bl: Compute brightness of LED linearly to human eye
  dt-bindings: pwm-backlight: Add a num-interpolation-steps property
  backlight: pwm_bl: Linear interpolation between brightness-levels
This commit is contained in:
Linus Torvalds 2018-08-20 15:41:37 -07:00
commit 61c4fc1eaf
4 changed files with 247 additions and 21 deletions
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34
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
View file

@ -3,13 +3,6 @@ pwm-backlight bindings
Required properties:
- compatible: "pwm-backlight"
- pwms: OF device-tree PWM specification (see PWM binding[0])
- brightness-levels: Array of distinct brightness levels. Typically these
are in the range from 0 to 255, but any range starting at 0 will do.
The actual brightness level (PWM duty cycle) will be interpolated
from these values. 0 means a 0% duty cycle (darkest/off), while the
last value in the array represents a 100% duty cycle (brightest).
- default-brightness-level: the default brightness level (index into the
array defined by the "brightness-levels" property)
- power-supply: regulator for supply voltage
Optional properties:
@ -21,6 +14,19 @@ Optional properties:
and enabling the backlight using GPIO.
- pwm-off-delay-ms: Delay in ms between disabling the backlight using GPIO
and setting PWM value to 0.
- brightness-levels: Array of distinct brightness levels. Typically these
are in the range from 0 to 255, but any range starting at
0 will do. The actual brightness level (PWM duty cycle)
will be interpolated from these values. 0 means a 0% duty
cycle (darkest/off), while the last value in the array
represents a 100% duty cycle (brightest).
- default-brightness-level: The default brightness level (index into the
array defined by the "brightness-levels" property).
- num-interpolated-steps: Number of interpolated steps between each value
of brightness-levels table. This way a high
resolution pwm duty cycle can be used without
having to list out every possible value in the
brightness-level array.
[0]: Documentation/devicetree/bindings/pwm/pwm.txt
[1]: Documentation/devicetree/bindings/gpio/gpio.txt
@ -39,3 +45,17 @@ Example:
post-pwm-on-delay-ms = <10>;
pwm-off-delay-ms = <10>;
};
Example using num-interpolation-steps:
backlight {
compatible = "pwm-backlight";
pwms = <&pwm 0 5000000>;
brightness-levels = <0 2048 4096 8192 16384 65535>;
num-interpolated-steps = <2048>;
default-brightness-level = <4096>;
power-supply = <&vdd_bl_reg>;
enable-gpios = <&gpio 58 0>;
};

1
drivers/video/backlight/adp8860_bl.c
View file

@ -690,6 +690,7 @@ static int adp8860_probe(struct i2c_client *client,
switch (ADP8860_MANID(reg_val)) {
case ADP8863_MANUFID:
data->gdwn_dis = !!pdata->gdwn_dis;
/* fall through */
case ADP8860_MANUFID:
data->en_ambl_sens = !!pdata->en_ambl_sens;
break;

232
drivers/video/backlight/pwm_bl.c
View file

@ -143,11 +143,116 @@ static const struct backlight_ops pwm_backlight_ops = {
};
#ifdef CONFIG_OF
#define PWM_LUMINANCE_SCALE 10000 /* luminance scale */
/* An integer based power function */
static u64 int_pow(u64 base, int exp)
{
u64 result = 1;
while (exp) {
if (exp & 1)
result *= base;
exp >>= 1;
base *= base;
}
return result;
}
/*
* CIE lightness to PWM conversion.
*
* The CIE 1931 lightness formula is what actually describes how we perceive
* light:
* Y = (L* / 902.3) if L* ≤ 0.08856
* Y = ((L* + 16) / 116)^3 if L* > 0.08856
*
* Where Y is the luminance, the amount of light coming out of the screen, and
* is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
* perceives the screen to be, and is a number between 0 and 100.
*
* The following function does the fixed point maths needed to implement the
* above formula.
*/
static u64 cie1931(unsigned int lightness, unsigned int scale)
{
u64 retval;
lightness *= 100;
if (lightness <= (8 * scale)) {
retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023);
} else {
retval = int_pow((lightness + (16 * scale)) / 116, 3);
retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
}
return retval;
}
/*
* Create a default correction table for PWM values to create linear brightness
* for LED based backlights using the CIE1931 algorithm.
*/
static
int pwm_backlight_brightness_default(struct device *dev,
struct platform_pwm_backlight_data *data,
unsigned int period)
{
unsigned int counter = 0;
unsigned int i, n;
u64 retval;
/*
* Count the number of bits needed to represent the period number. The
* number of bits is used to calculate the number of levels used for the
* brightness-levels table, the purpose of this calculation is have a
* pre-computed table with enough levels to get linear brightness
* perception. The period is divided by the number of bits so for a
* 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM
* we have 65535 / 16 = 4096 brightness levels.
*
* Note that this method is based on empirical testing on different
* devices with PWM of 8 and 16 bits of resolution.
*/
n = period;
while (n) {
counter += n % 2;
n >>= 1;
}
data->max_brightness = DIV_ROUND_UP(period, counter);
data->levels = devm_kcalloc(dev, data->max_brightness,
sizeof(*data->levels), GFP_KERNEL);
if (!data->levels)
return -ENOMEM;
/* Fill the table using the cie1931 algorithm */
for (i = 0; i < data->max_brightness; i++) {
retval = cie1931((i * PWM_LUMINANCE_SCALE) /
data->max_brightness, PWM_LUMINANCE_SCALE) *
period;
retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
if (retval > UINT_MAX)
return -EINVAL;
data->levels[i] = (unsigned int)retval;
}
data->dft_brightness = data->max_brightness / 2;
data->max_brightness--;
return 0;
}
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_steps = 0;
struct property *prop;
unsigned int *table;
int length;
u32 value;
int ret;
@ -157,16 +262,20 @@ static int pwm_backlight_parse_dt(struct device *dev,
memset(data, 0, sizeof(*data));
/* determine the number of brightness levels */
/*
* Determine the number of brightness levels, if this property is not
* set a default table of brightness levels will be used.
*/
prop = of_find_property(node, "brightness-levels", &length);
if (!prop)
return -EINVAL;
return 0;
data->max_brightness = 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;
data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
if (!data->levels)
@ -184,6 +293,84 @@ static int pwm_backlight_parse_dt(struct device *dev,
return ret;
data->dft_brightness = value;
/*
* This property is optional, if is set enables linear
* interpolation between each of the values of brightness levels
* and creates a new pre-computed table.
*/
of_property_read_u32(node, "num-interpolated-steps",
&num_steps);
/*
* Make sure that there is at least two entries in the
* brightness-levels table, otherwise we can't interpolate
* between two points.
*/
if (num_steps) {
if (data->max_brightness < 2) {
dev_err(dev, "can't interpolate\n");
return -EINVAL;
}
/*
* Recalculate the number of brightness levels, now
* 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++;
dev_dbg(dev, "new number of brightness levels: %d\n",
num_levels);
/*
* Create a new table of brightness levels with all the
* interpolated steps.
*/
size = sizeof(*table) * num_levels;
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++;
}
}
table[levels_count] = data->levels[i];
/*
* As we use interpolation lets remove current
* brightness levels table and replace for the
* new interpolated table.
*/
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--;
}
@ -211,6 +398,14 @@ static int pwm_backlight_parse_dt(struct device *dev,
{
return -ENODEV;
}
static
int pwm_backlight_brightness_default(struct device *dev,
struct platform_pwm_backlight_data *data,
unsigned int period)
{
return -ENODEV;
}
#endif
static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
@ -251,7 +446,9 @@ static int pwm_backlight_probe(struct platform_device *pdev)
struct backlight_device *bl;
struct device_node *node = pdev->dev.of_node;
struct pwm_bl_data *pb;
struct pwm_state state;
struct pwm_args pargs;
unsigned int i;
int ret;
if (!data) {
@ -276,17 +473,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
goto err_alloc;
}
if (data->levels) {
unsigned int i;
for (i = 0; i <= data->max_brightness; i++)
if (data->levels[i] > pb->scale)
pb->scale = data->levels[i];
pb->levels = data->levels;
} else
pb->scale = data->max_brightness;
pb->notify = data->notify;
pb->notify_after = data->notify_after;
pb->check_fb = data->check_fb;
@ -353,6 +539,26 @@ static int pwm_backlight_probe(struct platform_device *pdev)
dev_dbg(&pdev->dev, "got pwm for backlight\n");
if (!data->levels) {
/* Get the PWM period (in nanoseconds) */
pwm_get_state(pb->pwm, &state);
ret = pwm_backlight_brightness_default(&pdev->dev, data,
state.period);
if (ret < 0) {
dev_err(&pdev->dev,
"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];
pb->levels = data->levels;
}
/*
* FIXME: pwm_apply_args() should be removed when switching to
* the atomic PWM API.

1
include/linux/backlight.h
View file

@ -79,7 +79,6 @@ struct backlight_properties {
/* Backlight type */
enum backlight_type type;
/* Flags used to signal drivers of state changes */
/* Upper 4 bits are reserved for driver internal use */
unsigned int state;
#define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */