Date:   Wed, 8 Feb 2017 12:53:00 +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,
        daniel.thompson@...aro.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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