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Message-ID: <20170208125221.5qtvl4wksuhjtn7k@dell>
Date: Wed, 8 Feb 2017 12:52:21 +0000
From: Lee Jones <lee.jones@...aro.org>
To: Miłosz Rachwał <me@...ek7.pl>
Cc: Jingoo Han <jingoohan1@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: add DDC/CI brightness driver
Cc'ing Daniel Thompson, the new Maintainer.
On Sat, 21 Jan 2017, Miłosz Rachwał wrote:
> 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@...ek7.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@...ek7.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@...ek7.pl>");
> +MODULE_DESCRIPTION("VESA DDC/CI MCCS brightness driver");
> +MODULE_LICENSE("GPL");
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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