[PATCH v8 2/2] drivers: ddcci: upstream DDCCI driver

[Yusuf Khan]

This patch upstreams the DDCCI driver by Christoph Grenz into
the kernel. The original gitlab page is loacted at https://gitlab
.com/ddcci-driver-linux/ddcci-driver-linux/-/tree/master.

DDC/CI is a control protocol for monitor settings supported by most
monitors since about 2005. A chardev and sysfs interface is provided.
The seccond patch in this series provides a backlight driver using
DDC/CI.

Signed-off-by: Yusuf Khan <yusisamerican@xxxxxxxxx>
Signed-off-by: Christoph Grenz <christophg+lkml@xxxxxxxxxxxxx>
---
v2: Fix typos.

v3: Add documentation, move files around, replace semaphores with
mutexes, and replaced <asm-generic/fcntl.h> with <linux/fcntl.h>.
"imirkin"(which due to his involvement in the dri-devel irc channel
I cant help but assume to be a DRM developer) said that the DDC/CI
bus does not intefere with the buses that DRM is involved with.

v4: Move some documentation, fix grammer mistakes, remove usages of
likely(), and clarify some documentation.

v5: Fix grammer mistakes, remove usages of likely(), and clarify
some documentation.

v6: Change contact information to reference Christoph Grenz.

v7: Remove all instances of the unlikely() macro.

v8: Modify documentation to provide updated date and kernel
documentation, fix SPDX lines, use isalpha instead of redefining
logic, change maximum amount of bytes that can be written to be
conformant with DDC/CI specification, prevent userspace from holding
locks with the open file descriptor, remove ddcci_cdev_seek, dont
refine sysfs_emit() logic, use EXPORT_SYMBOL_GPL instead of
EXPORT_SYMBOL, remove ddcci_device_remove_void, remove module
paramaters and version, and split into 2 patches.
---
 drivers/video/backlight/Kconfig           |  11 +
 drivers/video/backlight/Makefile          |   1 +
 drivers/video/backlight/ddcci-backlight.c | 411 ++++++++++++++++++++++
 3 files changed, 423 insertions(+)
 create mode 100644 drivers/video/backlight/ddcci-backlight.c

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index e32694c13da5..7a26088c3c3f 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -289,6 +289,17 @@ config BACKLIGHT_QCOM_WLED
 	  If you have the Qualcomm PMIC, say Y to enable a driver for the
 	  WLED block. Currently it supports PM8941 and PMI8998.
 
+config BACKLIGHT_DDCCI
+	tristate "DDCCI Backlight Driver"
+	depends on DDCCI
+	help
+	  If you have a DDC/CI supporing monitor, say Y to enable a driver
+	  to control its backlight using DDC/CI. This could be useful if
+	  your monitor does not include a backlight driver. For this to be
+	  useful you need to enable DDCCI support which can be found in
+	  Device Drivers -> Character devices and that further depends on
+	  I2C.
+
 config BACKLIGHT_RT4831
 	tristate "Richtek RT4831 Backlight Driver"
 	depends on MFD_RT4831
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index cae2c83422ae..7bfb6e506b35 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -58,3 +58,4 @@ obj-$(CONFIG_BACKLIGHT_WM831X)		+= wm831x_bl.o
 obj-$(CONFIG_BACKLIGHT_ARCXCNN) 	+= arcxcnn_bl.o
 obj-$(CONFIG_BACKLIGHT_RAVE_SP)		+= rave-sp-backlight.o
 obj-$(CONFIG_BACKLIGHT_LED)		+= led_bl.o
+obj-$(CONFIG_BACKLIGHT_DDCCI)		+= ddcci-backlight.o
diff --git a/drivers/video/backlight/ddcci-backlight.c b/drivers/video/backlight/ddcci-backlight.c
new file mode 100644
index 000000000000..d37eb142311d
--- /dev/null
+++ b/drivers/video/backlight/ddcci-backlight.c
@@ -0,0 +1,411 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  DDC/CI monitor backlight driver
+ *
+ *  Copyright (c) 2015 Christoph Grenz
+ */
+
+/*
+ * 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.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/backlight.h>
+#include <linux/module.h>
+#include <linux/fb.h>
+#include <linux/sysfs.h>
+
+#include <linux/ddcci.h>
+
+
+#define DDCCI_COMMAND_READ	0x01	/* read ctrl value */
+#define DDCCI_REPLY_READ	0x02	/* read ctrl value reply */
+#define DDCCI_COMMAND_WRITE	0x03	/* write ctrl value */
+#define DDCCI_COMMAND_SAVE	0x0c	/* save current settings */
+
+#define DDCCI_MONITOR_LUMINANCE	0x10
+#define DDCCI_MONITOR_BACKLIGHT	0x13
+#define DDCCI_MONITOR_BL_WHITE		0x6B
+
+static bool convenience_symlink = true;
+
+struct ddcci_monitor_drv_data {
+	struct ddcci_device *device;
+	struct backlight_device *bl_dev;
+	struct device *fb_dev;
+	unsigned char used_vcp;
+};
+
+static int ddcci_monitor_writectrl(struct ddcci_device *device,
+				   unsigned char ctrl, unsigned short value)
+{
+	unsigned char buf[4];
+	int ret;
+
+	buf[0] = DDCCI_COMMAND_WRITE;
+	buf[1] = ctrl;
+	buf[2] = (value >> 8);
+	buf[3] = (value & 255);
+
+	ret = ddcci_device_write(device, true, buf, sizeof(buf));
+
+	return ret;
+}
+
+static int ddcci_monitor_readctrl(struct ddcci_device *device,
+				  unsigned char ctrl, unsigned short *value,
+				  unsigned short *maximum)
+{
+	int ret;
+	unsigned char buf[10];
+
+	buf[0] = DDCCI_COMMAND_READ;
+	buf[1] = ctrl;
+
+	ret = ddcci_device_writeread(device, true, buf, 2, sizeof(buf));
+	if (ret < 0)
+		return ret;
+
+	if (ret == 0)
+		return -ENOTSUPP;
+
+	if (ret == 8 && buf[0] == DDCCI_REPLY_READ && buf[2] == ctrl) {
+		if (value)
+			*value = buf[6] * 256 + buf[7];
+
+		if (maximum)
+			*maximum = buf[4] * 256 + buf[5];
+
+		if (buf[1] == 1)
+			return -ENOTSUPP;
+		if (buf[1] != 0)
+			return -EIO;
+		return 0;
+	}
+
+	return -EIO;
+}
+
+static int ddcci_backlight_check_fb(struct backlight_device *bl,
+				   struct fb_info *info)
+{
+	struct ddcci_monitor_drv_data *drv_data = bl_get_data(bl);
+
+	return drv_data->fb_dev == NULL || drv_data->fb_dev == info->dev;
+}
+
+static int ddcci_backlight_update_status(struct backlight_device *bl)
+{
+	struct ddcci_monitor_drv_data *drv_data = bl_get_data(bl);
+	int brightness = bl->props.brightness;
+	int ret;
+
+	if (bl->props.power != FB_BLANK_UNBLANK ||
+	    bl->props.state & BL_CORE_FBBLANK)
+		brightness = 0;
+
+	ret = ddcci_monitor_writectrl(drv_data->device, drv_data->used_vcp,
+				      brightness);
+	if (ret > 0)
+		ret = 0;
+	return ret;
+}
+
+static int ddcci_backlight_get_brightness(struct backlight_device *bl)
+{
+	unsigned short value = 0, maxval = 0;
+	int ret;
+	struct ddcci_monitor_drv_data *drv_data = bl_get_data(bl);
+
+	ret = ddcci_monitor_readctrl(drv_data->device, drv_data->used_vcp,
+				     &value, &maxval);
+	if (ret < 0)
+		return ret;
+
+	bl->props.brightness = value;
+	bl->props.max_brightness = maxval;
+	ret = value;
+
+	return ret;
+}
+
+static const struct backlight_ops ddcci_backlight_ops = {
+	.options	= 0,
+	.update_status	= ddcci_backlight_update_status,
+	.get_brightness = ddcci_backlight_get_brightness,
+	.check_fb	= ddcci_backlight_check_fb,
+};
+
+static const char *ddcci_monitor_vcp_name(unsigned char vcp)
+{
+	switch (vcp) {
+	case DDCCI_MONITOR_BL_WHITE:
+		return "backlight";
+	case DDCCI_MONITOR_LUMINANCE:
+		return "luminance";
+	default:
+		return "???";
+	}
+}
+
+static const char *ddcci_monitor_next_vcp_item(const char *ptr)
+{
+	int depth = 0;
+
+	/* Sanity check */
+	if (ptr == NULL || ptr[0] == '\0')
+		return NULL;
+
+	/* Find next white space outside of parentheses */
+	while ((ptr = strpbrk(ptr, " ()"))) {
+		if (!ptr || depth == INT_MAX)
+			return NULL;
+		else if (*ptr == '(')
+			depth++;
+		else if (depth > 0) {
+			if (*ptr == ')')
+				depth--;
+		} else
+			break;
+		++ptr;
+	}
+
+	/* Skip over whitespace */
+	ptr = skip_spaces(ptr);
+
+	/* Check if we're now at the end of the list */
+	if (*ptr == '\0' || *ptr == ')')
+		return NULL;
+
+	return ptr;
+}
+
+static bool ddcci_monitor_find_vcp(unsigned char vcp, const char *s)
+{
+	const char *ptr = s;
+	char vcp_hex[3];
+
+	/* Sanity check */
+	if (s == NULL || s[0] == '\0')
+		return false;
+
+	/* Create hex representation of VCP */
+	if (snprintf(vcp_hex, 3, "%02hhX", vcp) != 2) {
+		pr_err("snprintf failed to convert to hex. This should not happen.\n");
+		return false;
+	}
+
+	/* Search for it */
+	do {
+		if (strncasecmp(vcp_hex, ptr, 2) == 0) {
+			if (ptr[2] == ' ' || ptr[2] == '(' || ptr[2] == ')')
+				return true;
+		}
+	} while ((ptr = ddcci_monitor_next_vcp_item(ptr)));
+
+	return false;
+}
+
+static int ddcci_backlight_create_symlink(struct ddcci_device *ddcci_dev)
+{
+	int i, result;
+	struct device *dev = &ddcci_dev->dev;
+	struct kernfs_node *dirent;
+
+	for (i = 0; i < 3; ++i) {
+		dev = dev->parent;
+		if (!dev) {
+			dev_dbg(&ddcci_dev->dev, "failed to create convenience symlink: ancestor device not found\n");
+			return -ENOENT;
+		}
+	}
+	dirent = sysfs_get_dirent(dev->kobj.sd, "ddcci_backlight");
+	if (dirent) {
+		sysfs_put(dirent);
+		dev_dbg(&ddcci_dev->dev, "failed to create convenience symlink: %s/ddcci_backlight already exists\n", dev_name(dev));
+		return -EEXIST;
+	}
+
+	result = sysfs_create_link(&dev->kobj, &ddcci_dev->dev.kobj, "ddcci_backlight");
+	if (result == 0)
+		dev_dbg(&ddcci_dev->dev, "created symlink %s/ddcci_backlight\n", dev_name(dev));
+	else
+		dev_info(&ddcci_dev->dev, "failed to create convenience symlink: %d\n", result);
+	return result;
+}
+
+static int ddcci_backlight_remove_symlink(struct ddcci_device *ddcci_dev)
+{
+	int i;
+	struct device *dev = &ddcci_dev->dev;
+	struct kernfs_node *dirent;
+
+	for (i = 0; i < 3; ++i) {
+		dev = dev->parent;
+		if (!dev)
+			return -ENOENT;
+	}
+	dirent = sysfs_get_dirent(dev->kobj.sd, "ddcci_backlight");
+	if (!dirent)
+		return -ENOENT;
+
+	if ((dirent->flags & KERNFS_LINK) == 0) {
+		sysfs_put(dirent);
+		dev_dbg(&ddcci_dev->dev, "won't remove %s/ddcci_backlight: not a symlink\n", dev_name(dev));
+		return -EINVAL;
+	}
+
+	if (dirent->symlink.target_kn != ddcci_dev->dev.kobj.sd) {
+		sysfs_put(dirent);
+		dev_dbg(&ddcci_dev->dev, "won't remove %s/ddcci_backlight: we are not the link target\n", dev_name(dev));
+		return -EINVAL;
+	}
+
+	sysfs_put(dirent);
+
+	sysfs_remove_link(&dev->kobj, "ddcci_backlight");
+	dev_dbg(&ddcci_dev->dev, "removed symlink %s/ddcci_backlight\n", dev_name(dev));
+	return 0;
+}
+
+static int ddcci_monitor_probe(struct ddcci_device *dev,
+			       const struct ddcci_device_id *id)
+{
+	struct ddcci_monitor_drv_data *drv_data;
+	struct backlight_properties props;
+	struct backlight_device *bl = NULL;
+	int ret = 0;
+	bool support_luminance, support_bl_white;
+	unsigned short brightness = 0, max_brightness = 0;
+	const char *vcps;
+
+	dev_dbg(&dev->dev, "probing monitor backlight device\n");
+
+	/* Get VCP list */
+	vcps = ddcci_find_capstr_item(dev->capabilities, "vcp", NULL);
+	if (IS_ERR(vcps)) {
+		dev_info(&dev->dev,
+			 "monitor doesn't provide a list of supported controls.\n");
+		support_bl_white = support_luminance = true;
+	} else {
+		/* Check VCP list for supported VCPs */
+		support_bl_white = ddcci_monitor_find_vcp(DDCCI_MONITOR_BL_WHITE, vcps);
+		support_luminance = ddcci_monitor_find_vcp(DDCCI_MONITOR_LUMINANCE, vcps);
+		/* Fallback to trying if no support is found */
+		if (!support_bl_white && !support_luminance) {
+			dev_info(&dev->dev,
+				 "monitor doesn't announce support for backlight or luminance controls.\n");
+			support_bl_white = support_luminance = true;
+		}
+	}
+
+	/* Initialize driver data structure */
+	drv_data = devm_kzalloc(&dev->dev, sizeof(struct ddcci_monitor_drv_data),
+				GFP_KERNEL);
+	if (!drv_data)
+		return -ENOMEM;
+	drv_data->device = dev;
+
+	if (support_bl_white) {
+		/* Try getting backlight level */
+		dev_dbg(&dev->dev,
+			"trying to access \"backlight level white\" control\n");
+		ret = ddcci_monitor_readctrl(drv_data->device, DDCCI_MONITOR_BL_WHITE,
+						&brightness, &max_brightness);
+		if (ret < 0) {
+			if (ret == -ENOTSUPP)
+				dev_info(&dev->dev,
+					"monitor does not support reading backlight level\n");
+			else
+				goto err_free;
+		} else {
+			drv_data->used_vcp = DDCCI_MONITOR_BL_WHITE;
+		}
+	}
+
+	if (support_luminance && !drv_data->used_vcp) {
+		/* Try getting luminance */
+		dev_dbg(&dev->dev,
+			"trying to access \"luminance\" control\n");
+		ret = ddcci_monitor_readctrl(drv_data->device, DDCCI_MONITOR_LUMINANCE,
+					     &brightness, &max_brightness);
+		if (ret < 0) {
+			if (ret == -ENOTSUPP)
+				dev_info(&dev->dev,
+					"monitor does not support reading luminance\n");
+			else
+				goto err_free;
+		} else {
+			drv_data->used_vcp = DDCCI_MONITOR_LUMINANCE;
+		}
+		drv_data->used_vcp = DDCCI_MONITOR_LUMINANCE;
+	}
+
+	if (!drv_data->used_vcp)
+		goto err_free;
+
+	/* Create brightness device */
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = max_brightness;
+	props.brightness = brightness;
+	bl = devm_backlight_device_register(&dev->dev, dev_name(&dev->dev),
+					    &dev->dev, drv_data,
+					    &ddcci_backlight_ops, &props);
+	drv_data->bl_dev = bl;
+	if (IS_ERR(bl)) {
+		dev_err(&dev->dev, "failed to register backlight\n");
+		return PTR_ERR(bl);
+	}
+	dev_info(&dev->dev, "registered %s as backlight device %s\n",
+		 ddcci_monitor_vcp_name(drv_data->used_vcp),
+		 dev_name(&dev->dev));
+
+	if (convenience_symlink)
+		ddcci_backlight_create_symlink(dev);
+
+	goto end;
+err_free:
+	devm_kfree(&dev->dev, drv_data);
+end:
+	return ret;
+}
+
+static int ddcci_monitor_remove(struct ddcci_device *dev)
+{
+	dev_dbg(&dev->dev, "removing device\n");
+	ddcci_backlight_remove_symlink(dev);
+	return 0;
+}
+
+static struct ddcci_device_id ddcci_monitor_idtable[] = {
+	{ "monitor", DDCCI_ANY_ID, DDCCI_ANY_ID, DDCCI_ANY_ID, DDCCI_ANY_ID, 0 },
+	{}
+};
+
+static struct ddcci_driver ddcci_backlight_driver = {
+	.driver = {
+		.name	= "ddcci-backlight",
+		.owner	= THIS_MODULE,
+	},
+
+	.id_table	= ddcci_monitor_idtable,
+	.probe		= ddcci_monitor_probe,
+	.remove		= ddcci_monitor_remove,
+};
+
+module_ddcci_driver(ddcci_backlight_driver);
+
+/* Module parameter description */
+module_param(convenience_symlink, bool, 0644);
+MODULE_PARM_DESC(convenience_symlink, "add convenience symlink \"ddcci_backlight\" to ancestor device in sysfs (default true)");
+
+MODULE_AUTHOR("Christoph Grenz <christophg+lkml@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("DDC/CI generic monitor backlight driver");
+MODULE_VERSION("0.4.2");
+MODULE_LICENSE("GPL");
+
+MODULE_ALIAS("ddcci:monitor-*-*-*-*");
-- 
2.25.1