drm/solomon: Add SSD130x OLED displays I2C support

The ssd130x driver only provides the core support for these devices but it
does not have any bus transport logic. Add a driver to interface over I2C.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220214133710.3278506-5-javierm@redhat.com

drivers/gpu/drm/solomon/Kconfig

@@ -10,3 +10,12 @@ config DRM_SSD130X
 	  the appropriate bus transport in your chip also must be selected.
 
 	  If M is selected the module will be called ssd130x.
+
+config DRM_SSD130X_I2C
+	tristate "DRM support for Solomon SSD130x OLED displays (I2C bus)"
+	depends on DRM_SSD130X && I2C
+	select REGMAP_I2C
+	help
+	  Say Y here if the SSD130x OLED display is connected via I2C bus.
+
+	  If M is selected the module will be called ssd130x-i2c.

drivers/gpu/drm/solomon/Makefile

 obj-$(CONFIG_DRM_SSD130X)	+= ssd130x.o
+obj-$(CONFIG_DRM_SSD130X_I2C)	+= ssd130x-i2c.o

drivers/gpu/drm/solomon/ssd130x-i2c.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * DRM driver for Solomon SSD130x OLED displays (I2C bus)
+ *
+ * Copyright 2022 Red Hat Inc.
+ * Author: Javier Martinez Canillas <javierm@redhat.com>
+ *
+ * Based on drivers/video/fbdev/ssd1307fb.c
+ * Copyright 2012 Free Electrons
+ */
+#include <linux/i2c.h>
+#include <linux/module.h>
+
+#include "ssd130x.h"
+
+#define DRIVER_NAME	"ssd130x-i2c"
+#define DRIVER_DESC	"DRM driver for Solomon SSD130x OLED displays (I2C)"
+
+static const struct regmap_config ssd130x_i2c_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static int ssd130x_i2c_probe(struct i2c_client *client)
+{
+	struct ssd130x_device *ssd130x;
+	struct regmap *regmap;
+
+	regmap = devm_regmap_init_i2c(client, &ssd130x_i2c_regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	ssd130x = ssd130x_probe(&client->dev, regmap);
+	if (IS_ERR(ssd130x))
+		return PTR_ERR(ssd130x);
+
+	i2c_set_clientdata(client, ssd130x);
+
+	return 0;
+}
+
+static int ssd130x_i2c_remove(struct i2c_client *client)
+{
+	struct ssd130x_device *ssd130x = i2c_get_clientdata(client);
+
+	return ssd130x_remove(ssd130x);
+}
+
+static void ssd130x_i2c_shutdown(struct i2c_client *client)
+{
+	struct ssd130x_device *ssd130x = i2c_get_clientdata(client);
+
+	ssd130x_shutdown(ssd130x);
+}
+
+static struct ssd130x_deviceinfo ssd130x_ssd1305_deviceinfo = {
+	.default_vcomh = 0x34,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 7,
+};
+
+static struct ssd130x_deviceinfo ssd130x_ssd1306_deviceinfo = {
+	.default_vcomh = 0x20,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 8,
+	.need_chargepump = 1,
+};
+
+static struct ssd130x_deviceinfo ssd130x_ssd1307_deviceinfo = {
+	.default_vcomh = 0x20,
+	.default_dclk_div = 2,
+	.default_dclk_frq = 12,
+	.need_pwm = 1,
+};
+
+static struct ssd130x_deviceinfo ssd130x_ssd1309_deviceinfo = {
+	.default_vcomh = 0x34,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 10,
+};
+
+static const struct of_device_id ssd130x_of_match[] = {
+	{
+		.compatible = "solomon,ssd1305fb-i2c",
+		.data = &ssd130x_ssd1305_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1306fb-i2c",
+		.data = &ssd130x_ssd1306_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1307fb-i2c",
+		.data = &ssd130x_ssd1307_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1309fb-i2c",
+		.data = &ssd130x_ssd1309_deviceinfo,
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, ssd130x_of_match);
+
+static struct i2c_driver ssd130x_i2c_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = ssd130x_of_match,
+	},
+	.probe_new = ssd130x_i2c_probe,
+	.remove = ssd130x_i2c_remove,
+	.shutdown = ssd130x_i2c_shutdown,
+};
+module_i2c_driver(ssd130x_i2c_driver);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
+MODULE_LICENSE("GPL v2");