On Mon, Jul 20, 2020 at 09:25:20PM -0700, Alexandru Stan wrote:
> Whenever num-interpolated-steps was larger than the distance
> between 2 consecutive brightness levels the table would get really
> discontinuous. The slope of the interpolation would stick with
> integers only and if it was 0 the whole line segment would get skipped.
>
> Example settings:
> brightness-levels = <0 1 2 4 8 16 32 64 128 256>;
> num-interpolated-steps = <16>;
>
> The distances between 1 2 4 and 8 would be 1, and only starting with 16
> it would start to interpolate properly.
>
> Let's change it so there's always interpolation happening, even if
> there's no enough points available (read: values in the table would
> appear more than once). This should match the expected behavior much
> more closely.
>
> Reviewed-by: Douglas Anderson
> Reviewed-by: Matthias Kaehlcke
> Signed-off-by: Alexandru Stan
Apologies for the delay. Patch 2/3 meant I had some thinking to do...
and then the holiday's took their toll.
Overall this looks good, just some quibbles about broken 64-bit maths.
> ---
>
> drivers/video/backlight/pwm_bl.c | 70 ++--
> 1 file changed, 31 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/video/backlight/pwm_bl.c
> b/drivers/video/backlight/pwm_bl.c
> index 82b8d7594701..5193a72305a2 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -235,8 +235,7 @@ 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;
> @@ -265,12 +264,11 @@ 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)
> @@ -278,7 +276,7 @@ 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;
>
> @@ -303,7 +301,13 @@ 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;
> + u32 y1, y2;
> + s64 dx, dy;
dx should be 32-bit. It will be truncated to 32-bit when passed to
div_s64() so this type is actively misleading about how the maths
works.
> +
> + if (num_input_levels < 2) {
> dev_err(dev, "can't interpolate\n");
> return -EINVAL;
> }
> @@ -313,14 +317,7 @@ 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);
>
> @@ -332,24 +329,25 @@ 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++) {
> - valu
