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 <m...@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 <m...@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 <m...@milek7.pl>");
+MODULE_DESCRIPTION("VESA DDC/CI MCCS brightness driver");
+MODULE_LICENSE("GPL");
--
2.11.0
