Quick C program to calculate brightness to alpha pairs based on exposure adjustment driver (raphael values). Pretty sure there's an easier way but this was the only thing I thought of in the middle of the night

calculate_dc_dim_pairs.c

// Online C compiler to run C program online
// https://www.programiz.com/c-programming/online-compiler/
#include <stdio.h>

int main() {
    //  Formula to map value from A to B is (value - A_min) * (B_max - B_min) / (A_max - A_min) + B_min
    // A is coeffs      768 32768
    // B is dimming range  0 255

    // Below alues got from exposure adjustment driver
    // https://github.com/pwnrazr/kernel_raphael_sm8150/blob/715623fc27a33ac072603e9eb27c517aee663139/drivers/gpu/drm/msm/dsi-staging/exposure_adjustment.c
    #define ELVSS_OFF_THRESHOLD        420  // Constant backlight value
    #define EXPOSURE_ADJUSTMENT_MIN    768 

    /* PCC coefficient when exposure is 255 */
    #define EXPOSURE_ADJUSTMENT_MAX    32768
    /* Scale for the PCC coefficient with elvss backlight range */
    #define PCC_BACKLIGHT_SCALE \
    (EXPOSURE_ADJUSTMENT_MAX - EXPOSURE_ADJUSTMENT_MIN) / ELVSS_OFF_THRESHOLD
    
    #define min_dc_dimming_brightness 4
    
    // Device values(?)
    #define max_brightness 2047
    #define min_brightness 1
    #define step 1
    #define max_dim_range 255
    #define min_dim_range 0
    #define length 22

    int coeffs[max_brightness];
    int coeffs_remap[max_brightness];
    int coeffs_remap_invert[max_brightness];

    int bl_lvl, ea_coeff, min_step_num, max_step_num = 0;

    // Convert brightness level to coefficient
    for ( bl_lvl = 0; bl_lvl < max_brightness; bl_lvl = bl_lvl + step) 
    {
        coeffs[bl_lvl] =  bl_lvl * PCC_BACKLIGHT_SCALE + EXPOSURE_ADJUSTMENT_MIN;

        if(coeffs[bl_lvl] > EXPOSURE_ADJUSTMENT_MAX) {
            max_step_num = bl_lvl - min_brightness;
            printf("Max brightness before no DC Dim: %d\n", max_step_num);
            break;
        } 
    }

    //remap coefficients to dim values
    for ( int i = min_step_num; i < max_step_num; i = i + step){
        coeffs_remap[i] = (coeffs[i] - EXPOSURE_ADJUSTMENT_MIN) * (max_dim_range - min_dim_range) / (EXPOSURE_ADJUSTMENT_MAX - EXPOSURE_ADJUSTMENT_MIN) + min_dim_range;
    }
    
    //Invert coeffs in array
    for (int i = 0; i < max_step_num; i++) {
        coeffs_remap_invert[i] = coeffs_remap[max_step_num - i - 1];
    } 

    // Print values
    printf("brightness, alpha\n");
    for( int i = 0; i != length; i++ )
    {
        int brightness = i * (max_step_num - min_brightness) / (length - 1) + min_brightness;
        
        printf("%d %d\n", brightness, coeffs_remap_invert[brightness]);
    }
    printf("Min DC Dimming brightness pair:\n");
    printf("%d %d\n", min_dc_dimming_brightness, coeffs_remap_invert[min_dc_dimming_brightness]);
    return 0;
}