Add support for display panels built around the Novatek NT39016 display
controller, as found on e.g. the King Display KD035G6-54NT 24-bit
320x240 3.5" LCD panel which equips the GCW Zero open-source handheld
gaming console.

Signed-off-by: Paul Cercueil <p...@crapouillou.net>
Signed-off-by: Maarten ter Huurne <maar...@treewalker.org>
---

Notes:
    v2: - Don't cleanup backlight, as we use devm function to create it
        - Use backlight_enable / backlight_disable
        - Reorder includes
        - Use %d instead of %i to match other panel drivers
        - Bit 2 of NT39016_REG_SYSTEM register is 'reserved' and setting
          it doesn't seem to have any effect, so we don't set it anymore
        - Use macros for bits 0 and 1 of NT39016_REG_SYSTEM
        - Avoid 150ms sleep in nt39016_enable() if there is no backlight
          device
        - Include <linux/media-bus-format.h> instead of
          <uapi/linux/media-bus-format.h>
        - use /* sentinel */ in the last entry of the of_device_id table

 drivers/gpu/drm/panel/Kconfig                 |   9 +
 drivers/gpu/drm/panel/Makefile                |   1 +
 drivers/gpu/drm/panel/panel-novatek-nt39016.c | 359 ++++++++++++++++++
 3 files changed, 369 insertions(+)
 create mode 100644 drivers/gpu/drm/panel/panel-novatek-nt39016.c

diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
index d9d931aa6e26..17959876621f 100644
--- a/drivers/gpu/drm/panel/Kconfig
+++ b/drivers/gpu/drm/panel/Kconfig
@@ -111,6 +111,15 @@ config DRM_PANEL_LG_LG4573
          Say Y here if you want to enable support for LG4573 RGB panel.
          To compile this driver as a module, choose M here.
 
+config DRM_PANEL_NOVATEK_NT39016
+       tristate "Novatek NT39016 RGB/SPI panel"
+       depends on OF && SPI
+       depends on BACKLIGHT_CLASS_DEVICE
+       select REGMAP_SPI
+       help
+         Say Y here if you want to enable support for the panels built
+         around the Novatek NT39016 display controller.
+
 config DRM_PANEL_OLIMEX_LCD_OLINUXINO
        tristate "Olimex LCD-OLinuXino panel"
        depends on OF
diff --git a/drivers/gpu/drm/panel/Makefile b/drivers/gpu/drm/panel/Makefile
index fb0cb3aaa9e6..f8709d280d61 100644
--- a/drivers/gpu/drm/panel/Makefile
+++ b/drivers/gpu/drm/panel/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_DRM_PANEL_INNOLUX_P079ZCA) += 
panel-innolux-p079zca.o
 obj-$(CONFIG_DRM_PANEL_JDI_LT070ME05000) += panel-jdi-lt070me05000.o
 obj-$(CONFIG_DRM_PANEL_KINGDISPLAY_KD097D04) += panel-kingdisplay-kd097d04.o
 obj-$(CONFIG_DRM_PANEL_LG_LG4573) += panel-lg-lg4573.o
+obj-$(CONFIG_DRM_PANEL_NOVATEK_NT39016) += panel-novatek-nt39016.o
 obj-$(CONFIG_DRM_PANEL_OLIMEX_LCD_OLINUXINO) += panel-olimex-lcd-olinuxino.o
 obj-$(CONFIG_DRM_PANEL_ORISETECH_OTM8009A) += panel-orisetech-otm8009a.o
 obj-$(CONFIG_DRM_PANEL_OSD_OSD101T2587_53TS) += panel-osd-osd101t2587-53ts.o
diff --git a/drivers/gpu/drm/panel/panel-novatek-nt39016.c 
b/drivers/gpu/drm/panel/panel-novatek-nt39016.c
new file mode 100644
index 000000000000..4a1c172b57c3
--- /dev/null
+++ b/drivers/gpu/drm/panel/panel-novatek-nt39016.c
@@ -0,0 +1,359 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Novatek NT39016 TFT LCD panel driver
+ *
+ * Copyright (C) 2017, Maarten ter Huurne <maar...@treewalker.org>
+ * Copyright (C) 2019, Paul Cercueil <p...@crapouillou.net>
+ */
+
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/media-bus-format.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+
+#include <drm/drm_modes.h>
+#include <drm/drm_panel.h>
+
+
+enum nt39016_regs {
+       NT39016_REG_SYSTEM,
+       NT39016_REG_TIMING,
+       NT39016_REG_OP,
+       NT39016_REG_DATA_IN,
+       NT39016_REG_SRC_TIMING_DELAY,
+       NT39016_REG_GATE_TIMING_DELAY,
+       NT39016_REG_RESERVED,
+       NT39016_REG_INITIAL_FUNC,
+       NT39016_REG_CONTRAST,
+       NT39016_REG_BRIGHTNESS,
+       NT39016_REG_HUE_SATURATION,
+       NT39016_REG_RB_SUBCONTRAST,
+       NT39016_REG_R_SUBBRIGHTNESS,
+       NT39016_REG_B_SUBBRIGHTNESS,
+       NT39016_REG_VCOMDC,
+       NT39016_REG_VCOMAC,
+       NT39016_REG_VGAM2,
+       NT39016_REG_VGAM34,
+       NT39016_REG_VGAM56,
+       NT39016_REG_VCOMDC_TRIM = 0x1e,
+       NT39016_REG_DISPLAY_MODE = 0x20,
+};
+
+#define NT39016_SYSTEM_RESET_N BIT(0)
+#define NT39016_SYSTEM_STANDBY BIT(1)
+
+struct nt39016_panel_info {
+       struct drm_display_mode display_mode;
+       u16 width_mm, height_mm;
+       u32 bus_format, bus_flags;
+};
+
+struct nt39016 {
+       struct drm_panel drm_panel;
+       struct device *dev;
+       struct regmap *map;
+       struct regulator *supply;
+       const struct nt39016_panel_info *panel_info;
+
+       struct gpio_desc *reset_gpio;
+
+       struct backlight_device *backlight;
+};
+
+static inline struct nt39016 *to_nt39016(struct drm_panel *panel)
+{
+       return container_of(panel, struct nt39016, drm_panel);
+}
+
+#define RV(REG, VAL) { .reg = (REG), .def = (VAL), .delay_us = 2 }
+static const struct reg_sequence nt39016_panel_regs[] = {
+       RV(NT39016_REG_SYSTEM, 0x00),
+       RV(NT39016_REG_TIMING, 0x00),
+       RV(NT39016_REG_OP, 0x03),
+       RV(NT39016_REG_DATA_IN, 0xCC),
+       RV(NT39016_REG_SRC_TIMING_DELAY, 0x46),
+       RV(NT39016_REG_GATE_TIMING_DELAY, 0x05),
+       RV(NT39016_REG_RESERVED, 0x00),
+       RV(NT39016_REG_INITIAL_FUNC, 0x00),
+       RV(NT39016_REG_CONTRAST, 0x08),
+       RV(NT39016_REG_BRIGHTNESS, 0x40),
+       RV(NT39016_REG_HUE_SATURATION, 0x88),
+       RV(NT39016_REG_RB_SUBCONTRAST, 0x88),
+       RV(NT39016_REG_R_SUBBRIGHTNESS, 0x20),
+       RV(NT39016_REG_B_SUBBRIGHTNESS, 0x20),
+       RV(NT39016_REG_VCOMDC, 0x67),
+       RV(NT39016_REG_VCOMAC, 0xA4),
+       RV(NT39016_REG_VGAM2, 0x04),
+       RV(NT39016_REG_VGAM34, 0x24),
+       RV(NT39016_REG_VGAM56, 0x24),
+       RV(NT39016_REG_DISPLAY_MODE, 0x00),
+};
+#undef RV
+
+static const struct regmap_range nt39016_regmap_no_ranges[] = {
+       regmap_reg_range(0x13, 0x1D),
+       regmap_reg_range(0x1F, 0x1F),
+};
+
+static const struct regmap_access_table nt39016_regmap_access_table = {
+       .no_ranges = nt39016_regmap_no_ranges,
+       .n_no_ranges = ARRAY_SIZE(nt39016_regmap_no_ranges),
+};
+
+static const struct regmap_config nt39016_regmap_config = {
+       .reg_bits = 6,
+       .pad_bits = 2,
+       .val_bits = 8,
+
+       .max_register = NT39016_REG_DISPLAY_MODE,
+       .wr_table = &nt39016_regmap_access_table,
+       .write_flag_mask = 0x02,
+
+       .cache_type = REGCACHE_FLAT,
+};
+
+static int nt39016_prepare(struct drm_panel *drm_panel)
+{
+       struct nt39016 *panel = to_nt39016(drm_panel);
+       int err;
+
+       err = regulator_enable(panel->supply);
+       if (err) {
+               dev_err(panel->dev, "Failed to enable power supply: %d", err);
+               return err;
+       }
+
+       /*
+        * Reset the NT39016.
+        * The documentation says the reset pulse should be at least 40 us to
+        * pass the glitch filter, but when testing I see some resets fail and
+        * some succeed when using a 70 us delay, so we use 100 us instead.
+        */
+       gpiod_set_value_cansleep(panel->reset_gpio, 1);
+       usleep_range(100, 1000);
+       gpiod_set_value_cansleep(panel->reset_gpio, 0);
+       udelay(2);
+
+       /* Init all registers. */
+       err = regmap_multi_reg_write(panel->map, nt39016_panel_regs,
+                                    ARRAY_SIZE(nt39016_panel_regs));
+       if (err) {
+               dev_err(panel->dev, "Failed to init registers: %d", err);
+               goto err_disable_regulator;
+       }
+
+       return 0;
+
+err_disable_regulator:
+       regulator_disable(panel->supply);
+       return err;
+}
+
+static int nt39016_unprepare(struct drm_panel *drm_panel)
+{
+       struct nt39016 *panel = to_nt39016(drm_panel);
+
+       gpiod_set_value_cansleep(panel->reset_gpio, 1);
+
+       regulator_disable(panel->supply);
+
+       return 0;
+}
+
+static int nt39016_enable(struct drm_panel *drm_panel)
+{
+       struct nt39016 *panel = to_nt39016(drm_panel);
+       int ret;
+
+       ret = regmap_write(panel->map, NT39016_REG_SYSTEM,
+                          NT39016_SYSTEM_RESET_N | NT39016_SYSTEM_STANDBY);
+       if (ret) {
+               dev_err(panel->dev, "Unable to enable panel: %d", ret);
+               return ret;
+       }
+
+       if (panel->backlight) {
+               /* Wait for the picture to be ready before enabling backlight */
+               msleep(150);
+
+               ret = backlight_enable(panel->backlight);
+       }
+
+       return ret;
+}
+
+static int nt39016_disable(struct drm_panel *drm_panel)
+{
+       struct nt39016 *panel = to_nt39016(drm_panel);
+       int err;
+
+       backlight_disable(panel->backlight);
+
+       err = regmap_write(panel->map, NT39016_REG_SYSTEM,
+                          NT39016_SYSTEM_RESET_N);
+       if (err) {
+               dev_err(panel->dev, "Unable to disable panel: %d", err);
+               return err;
+       }
+
+       return 0;
+}
+
+static int nt39016_get_modes(struct drm_panel *drm_panel)
+{
+       struct nt39016 *panel = to_nt39016(drm_panel);
+       const struct nt39016_panel_info *panel_info = panel->panel_info;
+       struct drm_connector *connector = drm_panel->connector;
+       struct drm_display_mode *mode;
+
+       mode = drm_mode_duplicate(drm_panel->drm, &panel_info->display_mode);
+       if (!mode)
+               return -ENOMEM;
+
+       drm_mode_set_name(mode);
+
+       mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
+       drm_mode_probed_add(connector, mode);
+
+       connector->display_info.bpc = 8;
+       connector->display_info.width_mm = panel_info->width_mm;
+       connector->display_info.height_mm = panel_info->height_mm;
+
+       drm_display_info_set_bus_formats(&connector->display_info,
+                                        &panel_info->bus_format, 1);
+       connector->display_info.bus_flags = panel_info->bus_flags;
+
+       return 1;
+}
+
+static const struct drm_panel_funcs nt39016_funcs = {
+       .prepare        = nt39016_prepare,
+       .unprepare      = nt39016_unprepare,
+       .enable         = nt39016_enable,
+       .disable        = nt39016_disable,
+       .get_modes      = nt39016_get_modes,
+};
+
+static int nt39016_probe(struct spi_device *spi)
+{
+       struct device *dev = &spi->dev;
+       struct nt39016 *panel;
+       int err;
+
+       panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
+       if (!panel)
+               return -ENOMEM;
+
+       panel->dev = dev;
+       spi_set_drvdata(spi, panel);
+
+       panel->panel_info = of_device_get_match_data(dev);
+       if (!panel->panel_info)
+               return -EINVAL;
+
+       panel->supply = devm_regulator_get(dev, "power");
+       if (IS_ERR(panel->supply)) {
+               dev_err(dev, "Failed to get power supply");
+               return PTR_ERR(panel->supply);
+       }
+
+       panel->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
+       if (IS_ERR(panel->reset_gpio)) {
+               dev_err(dev, "Failed to get reset GPIO");
+               return PTR_ERR(panel->reset_gpio);
+       }
+
+       spi->bits_per_word = 8;
+       spi->mode = SPI_MODE_3 | SPI_3WIRE;
+       err = spi_setup(spi);
+       if (err) {
+               dev_err(dev, "Failed to setup SPI");
+               return err;
+       }
+
+       panel->map = devm_regmap_init_spi(spi, &nt39016_regmap_config);
+       if (IS_ERR(panel->map)) {
+               dev_err(dev, "Failed to init regmap");
+               return PTR_ERR(panel->map);
+       }
+
+       panel->backlight = devm_of_find_backlight(dev);
+       if (IS_ERR(panel->backlight)) {
+               err = PTR_ERR(panel->backlight);
+               if (err != -EPROBE_DEFER)
+                       dev_err(dev, "Failed to get backlight handle");
+               return err;
+       }
+
+       drm_panel_init(&panel->drm_panel);
+       panel->drm_panel.dev = dev;
+       panel->drm_panel.funcs = &nt39016_funcs;
+
+       err = drm_panel_add(&panel->drm_panel);
+       if (err < 0) {
+               dev_err(dev, "Failed to register panel");
+               return err;
+       }
+
+       return 0;
+}
+
+static int nt39016_remove(struct spi_device *spi)
+{
+       struct nt39016 *panel = spi_get_drvdata(spi);
+
+       drm_panel_remove(&panel->drm_panel);
+
+       nt39016_disable(&panel->drm_panel);
+       nt39016_unprepare(&panel->drm_panel);
+
+       return 0;
+}
+
+static const struct nt39016_panel_info kd035g6_info = {
+       .display_mode = {
+               .clock = 6000,
+               .hdisplay = 320,
+               .hsync_start = 320 + 10,
+               .hsync_end = 320 + 10 + 50,
+               .htotal = 320 + 10 + 50 + 20,
+               .vdisplay = 240,
+               .vsync_start = 240 + 5,
+               .vsync_end = 240 + 5 + 1,
+               .vtotal = 240 + 5 + 1 + 4,
+               .vrefresh = 60,
+               .flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
+       },
+       .width_mm = 71,
+       .height_mm = 53,
+       .bus_format = MEDIA_BUS_FMT_RGB888_1X24,
+       .bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE,
+};
+
+static const struct of_device_id nt39016_of_match[] = {
+       { .compatible = "kingdisplay,kd035g6-54nt", .data = &kd035g6_info },
+       { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, nt39016_of_match);
+
+static struct spi_driver nt39016_driver = {
+       .driver = {
+               .name = "nt39016",
+               .of_match_table = nt39016_of_match,
+       },
+       .probe = nt39016_probe,
+       .remove = nt39016_remove,
+};
+
+module_spi_driver(nt39016_driver);
+
+MODULE_AUTHOR("Maarten ter Huurne <maar...@treewalker.org>");
+MODULE_AUTHOR("Paul Cercueil <p...@crapouillou.net>");
+MODULE_LICENSE("GPL v2");
-- 
2.21.0.593.g511ec345e18

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