[PATCH] backlight: add DDC/CI brightness driver

From: "Miłosz Rachwał" <me@milek7.pl>
To: Jingoo Han <jingoohan1@gmail.com>, Lee Jones <lee.jones@linaro.org>
Cc: "Miłosz Rachwał" <me@milek7.pl>, linux-kernel@vger.kernel.org
Subject: [PATCH] backlight: add DDC/CI brightness driver
Date: Sat, 21 Jan 2017 19:31:51 +0100	[thread overview]
Message-ID: <20170121183151.8313-1-me@milek7.pl> (raw)

This patch contains driver for exposing VESA DDC/CI MCCS brightness
settings via kernel backlight API. This allows to control monitor
brightness using standard software which uses /sys/class/backlight/
interface, same as for laptop backlight drivers.
Because some monitors don't correctly implement DDC/CI standard module
parameter allows to override maximum brightness value reported by
monitor.
This module doesn't support autodetection, so driver must be manually
instantiated on monitor I²C bus under 0x37 address.

Signed-off-by: Miłosz Rachwał <me@milek7.pl>
---
 drivers/video/backlight/Kconfig    |   7 ++
 drivers/video/backlight/Makefile   |   1 +
 drivers/video/backlight/ddcci_bl.c | 128 +++++++++++++++++++++++++++++++++++++
 3 files changed, 136 insertions(+)
 create mode 100644 drivers/video/backlight/ddcci_bl.c

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index 5ffa4b4e..cce62832 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -460,6 +460,13 @@ config BACKLIGHT_BD6107
 	help
 	  If you have a Rohm BD6107 say Y to enable the backlight driver.
 
+config BACKLIGHT_DDCCI
+	tristate "VESA DDC/CI MCCS brightness driver"
+	depends on BACKLIGHT_CLASS_DEVICE && I2C
+	default m
+	help
+	  This supports brightness control via VESA DDC/CI MCCS.
+
 endif # BACKLIGHT_CLASS_DEVICE
 
 endif # BACKLIGHT_LCD_SUPPORT
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index 16ec534c..2e5352aa 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_BACKLIGHT_CARILLO_RANCH)	+= cr_bllcd.o
 obj-$(CONFIG_BACKLIGHT_CLASS_DEVICE)	+= backlight.o
 obj-$(CONFIG_BACKLIGHT_DA903X)		+= da903x_bl.o
 obj-$(CONFIG_BACKLIGHT_DA9052)		+= da9052_bl.o
+obj-$(CONFIG_BACKLIGHT_DDCCI)		+= ddcci_bl.o
 obj-$(CONFIG_BACKLIGHT_EP93XX)		+= ep93xx_bl.o
 obj-$(CONFIG_BACKLIGHT_GENERIC)		+= generic_bl.o
 obj-$(CONFIG_BACKLIGHT_GPIO)		+= gpio_backlight.o
diff --git a/drivers/video/backlight/ddcci_bl.c b/drivers/video/backlight/ddcci_bl.c
new file mode 100644
index 00000000..c314cbc8
--- /dev/null
+++ b/drivers/video/backlight/ddcci_bl.c
@@ -0,0 +1,128 @@
+/*
+ * VESA DDC/CI MCCS brightness driver
+ *
+ * Copyright (C) 2017 Miłosz Rachwał <me@milek7.pl>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/backlight.h>
+#include <linux/delay.h>
+
+static int maxbr;
+module_param(maxbr, int, 0644);
+MODULE_PARM_DESC(maxbr, "Override maximum brightness value specified by monitor");
+
+static int ddcci_update_status(struct backlight_device *bl)
+{
+	struct i2c_client *client = bl_get_data(bl);
+
+	char buf[] = { 0x51, 0x84, 0x03, 0x10, 0x00, 0x00, 0x00 };
+	buf[4] = bl->props.brightness >> 8;
+	buf[5] = bl->props.brightness;
+	buf[6] = (client->addr << 1) ^ 0xC6 ^ buf[4] ^ buf[5];
+
+	i2c_master_send(client, buf, 7);
+	msleep(50);
+
+	return 0;
+}
+
+static int ddcci_read(struct i2c_client *client, struct backlight_properties *props, int init)
+{
+	int i;
+	char xor;
+
+	char buf[11] = { 0x51, 0x82, 0x01, 0x10, 0x00 };
+	buf[4] = (client->addr << 1) ^ 0xC2;
+
+	i2c_master_send(client, buf, 5);
+	msleep(40);
+	i2c_master_recv(client, buf, 11);
+
+	if (buf[3] != 0)
+		goto fail;
+
+	xor = 0x50;
+	for (i = 0; i < 11; i++)
+		xor ^= buf[i];
+
+	if (xor)
+		goto fail;
+
+	if (init) {
+		if (maxbr)
+			props->max_brightness = maxbr;
+		else
+			props->max_brightness = (buf[6] << 8) | buf[7];
+	}
+	props->brightness = (buf[8] << 8) | buf[9];
+
+	return 0;
+
+fail:
+	dev_err(&client->dev, "failed to read brightness");
+	return -1;
+}
+
+static int ddcci_get_brightness(struct backlight_device *bl)
+{
+	struct i2c_client *client = bl_get_data(bl);
+
+	ddcci_read(client, &bl->props, 0);
+	return bl->props.brightness;
+}
+
+static const struct backlight_ops ddcci_ops = {
+	.update_status = ddcci_update_status,
+	.get_brightness = ddcci_get_brightness
+};
+
+static int ddcci_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+	struct backlight_properties props;
+	int retry;
+	char name[20];
+
+	memset(&props, 0, sizeof(struct backlight_properties));
+	props.type = BACKLIGHT_FIRMWARE;
+	snprintf(name, 20, "ddcci_%s", dev_name(&client->dev));
+
+	for (retry = 0; retry < 3; retry++) {
+		if (ddcci_read(client, &props, 1) >= 0) {
+			devm_backlight_device_register(&client->dev, name, &client->dev, client, &ddcci_ops, &props);
+			return 0;
+		}
+	}
+
+	return -1;
+}
+
+static int ddcci_remove(struct i2c_client *client)
+{
+	return 0;
+}
+
+static struct i2c_device_id ddcci_idtable[] = {
+	{ "ddcci_bl", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ddcci_idtable);
+
+static struct i2c_driver ddcci_driver = {
+	.driver = { .name = "ddcci_bl" },
+	.id_table = ddcci_idtable,
+	.probe = ddcci_probe,
+	.remove = ddcci_remove
+};
+module_i2c_driver(ddcci_driver);
+
+MODULE_AUTHOR("Miłosz Rachwał <me@milek7.pl>");
+MODULE_DESCRIPTION("VESA DDC/CI MCCS brightness driver");
+MODULE_LICENSE("GPL");
-- 
2.11.0
