// SPDX-License-Identifier: GPL-2.0+
/*
 * FB driver for the SSD1325 OLED Controller
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/gpio/consumer.h>
#include <linux/delay.h>

#include "fbtft.h"

#define DRVNAME         "fb_ssd1325"

#define WIDTH 128
#define HEIGHT 64
#define GAMMA_NUM   1
#define GAMMA_LEN   15
#define DEFAULT_GAMMA "7 1 1 1 1 2 2 3 3 4 4 5 5 6 6"

/*
 * write_reg() caveat:
 *
 *    This doesn't work because D/C has to be LOW for both values:
 *      write_reg(par, val1, val2);
 *
 *    Do it like this:
 *      write_reg(par, val1);
 *      write_reg(par, val2);
 */

/* Init sequence taken from the Adafruit SSD1306 Arduino library */
static int init_display(struct fbtft_par *par)
{
        par->fbtftops.reset(par);

        write_reg(par, 0xb3);
        write_reg(par, 0xf0);
        write_reg(par, 0xae);
        write_reg(par, 0xa1);
        write_reg(par, 0x00);
        write_reg(par, 0xa8);
        write_reg(par, 0x3f);
        write_reg(par, 0xa0);
        write_reg(par, 0x45);
        write_reg(par, 0xa2);
        write_reg(par, 0x40);
        write_reg(par, 0x75);
        write_reg(par, 0x00);
        write_reg(par, 0x3f);
        write_reg(par, 0x15);
        write_reg(par, 0x00);
        write_reg(par, 0x7f);
        write_reg(par, 0xa4);
        write_reg(par, 0xaf);

        return 0;
}

static uint8_t rgb565_to_g16(u16 pixel)
{
        u16 b = pixel & 0x1f;
        u16 g = (pixel & (0x3f << 5)) >> 5;
        u16 r = (pixel & (0x1f << (5 + 6))) >> (5 + 6);

        pixel = (299 * r + 587 * g + 114 * b) / 195;
        if (pixel > 255)
                pixel = 255;
        return (uint8_t)pixel / 16;
}

static void set_addr_win(struct fbtft_par *par, int xs, int ys, int xe, int ye)
{
        write_reg(par, 0x75);
        write_reg(par, 0x00);
        write_reg(par, 0x3f);
        write_reg(par, 0x15);
        write_reg(par, 0x00);
        write_reg(par, 0x7f);
}

static int blank(struct fbtft_par *par, bool on)
{
        if (on)
                write_reg(par, 0xAE);
        else
                write_reg(par, 0xAF);
        return 0;
}

/*
 * Grayscale Lookup Table
 * GS1 - GS15
 * The "Gamma curve" contains the relative values between the entries
 * in the Lookup table.
 *
 * 0 = Setting of GS1 < Setting of GS2 < Setting of GS3.....<
 * Setting of GS14 < Setting of GS15
 */
static int set_gamma(struct fbtft_par *par, u32 *curves)
{
        int i;

        for (i = 0; i < GAMMA_LEN; i++) {
                if (i > 0 && curves[i] < 1) {
                        dev_err(par->info->device,
                                "Illegal value in Grayscale Lookup Table at index %d.\n"
                                "Must be greater than 0\n", i);
                        return -EINVAL;
                }
                if (curves[i] > 7) {
                        dev_err(par->info->device,
                                "Illegal value(s) in Grayscale Lookup Table.\n"
                                "At index=%d, the accumulated value has exceeded 7\n",
                                i);
                        return -EINVAL;
                }
        }
        write_reg(par, 0xB8);
        for (i = 0; i < 8; i++)
                write_reg(par, (curves[i] & 0xFF));
        return 0;
}

static int write_vmem(struct fbtft_par *par, size_t offset, size_t len)
{
        u16 *vmem16 = (u16 *)par->info->screen_buffer;
        u8 *buf = par->txbuf.buf;
        u8 n1;
        u8 n2;
        int y, x;
        int ret;

        for (x = 0; x < par->info->var.xres; x++) {
                if (x % 2)
                        continue;
                for (y = 0; y < par->info->var.yres; y++) {
                        n1 = rgb565_to_g16(vmem16[y * par->info->var.xres + x]);
                        n2 = rgb565_to_g16(vmem16
                                           [y * par->info->var.xres + x + 1]);
                        *buf = (n1 << 4) | n2;
                        buf++;
                }
        }

        gpiod_set_value(par->gpio.dc, 1);

        /* Write data */
        ret = par->fbtftops.write(par, par->txbuf.buf,
                                par->info->var.xres * par->info->var.yres / 2);
        if (ret < 0)
                dev_err(par->info->device,
                        "%s: write failed and returned: %d\n", __func__, ret);

        return ret;
}

static struct fbtft_display display = {
        .regwidth = 8,
        .width = WIDTH,
        .height = HEIGHT,
        .txbuflen = WIDTH * HEIGHT / 2,
        .gamma_num = GAMMA_NUM,
        .gamma_len = GAMMA_LEN,
        .gamma = DEFAULT_GAMMA,
        .fbtftops = {
                .write_vmem = write_vmem,
                .init_display = init_display,
                .set_addr_win = set_addr_win,
                .blank = blank,
                .set_gamma = set_gamma,
        },
};

FBTFT_REGISTER_DRIVER(DRVNAME, "solomon,ssd1325", &display);

MODULE_ALIAS("spi:" DRVNAME);
MODULE_ALIAS("platform:" DRVNAME);
MODULE_ALIAS("spi:ssd1325");
MODULE_ALIAS("platform:ssd1325");

MODULE_DESCRIPTION("SSD1325 OLED Driver");
MODULE_AUTHOR("Alexey Mednyy");
MODULE_LICENSE("GPL");