The OV5647 sensor from Omnivision supports up to 2592x1944 @ 15 fps, RAW 8
and RAW 10 output formats, and MIPI CSI-2 interface.
The driver adds support for 640x480 RAW 8.
Signed-off-by: Ramiro Oliveira <roliveir@xxxxxxxxxxxx>
---
MAINTAINERS | 7 +
drivers/media/i2c/Kconfig | 11 +
drivers/media/i2c/Makefile | 1 +
drivers/media/i2c/ov5647.c | 636 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 655 insertions(+)
create mode 100644 drivers/media/i2c/ov5647.c
diff --git a/MAINTAINERS b/MAINTAINERS
index b9e80b6bb745..630482636898 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9141,6 +9141,13 @@ M: Harald Welte <laforge@xxxxxxxxxxxx>
S: Maintained
F: drivers/char/pcmcia/cm4040_cs.*
+OMNIVISION OV5647 SENSOR DRIVER
+M: Ramiro Oliveira <roliveir@xxxxxxxxxxxx>
+L: linux-media@xxxxxxxxxxxxxxx
+T: git git://linuxtv.org/media_tree.git
+S: Maintained
+F: drivers/media/i2c/ov5647.c
+
OMNIVISION OV7670 SENSOR DRIVER
M: Jonathan Corbet <corbet@xxxxxxx>
L: linux-media@xxxxxxxxxxxxxxx
diff --git a/drivers/media/i2c/Kconfig b/drivers/media/i2c/Kconfig
index cee1dae6e014..8435b99f38bc 100644
--- a/drivers/media/i2c/Kconfig
+++ b/drivers/media/i2c/Kconfig
@@ -531,6 +531,17 @@ config VIDEO_OV2659
To compile this driver as a module, choose M here: the
module will be called ov2659.
+config VIDEO_OV5647
+ tristate "OmniVision OV5647 sensor support"
+ depends on I2C && VIDEO_V4L2 && VIDEO_V4L2_SUBDEV_API
+ depends on MEDIA_CAMERA_SUPPORT
+ ---help---
+ This is a Video4Linux2 sensor-level driver for the OmniVision
+ OV5647 camera.
+
+ To compile this driver as a module, choose M here: the
+ module will be called ov5647.
+
config VIDEO_OV7640
tristate "OmniVision OV7640 sensor support"
depends on I2C && VIDEO_V4L2
diff --git a/drivers/media/i2c/Makefile b/drivers/media/i2c/Makefile
index 5bc7bbeb5499..ef2ccf65f94c 100644
--- a/drivers/media/i2c/Makefile
+++ b/drivers/media/i2c/Makefile
@@ -83,3 +83,4 @@ obj-$(CONFIG_VIDEO_IR_I2C) += ir-kbd-i2c.o
obj-$(CONFIG_VIDEO_ML86V7667) += ml86v7667.o
obj-$(CONFIG_VIDEO_OV2659) += ov2659.o
obj-$(CONFIG_VIDEO_TC358743) += tc358743.o
+obj-$(CONFIG_VIDEO_OV5647) += ov5647.o
diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
new file mode 100644
index 000000000000..07de127e84b2
--- /dev/null
+++ b/drivers/media/i2c/ov5647.c
@@ -0,0 +1,636 @@
+/*
+ * A V4L2 driver for OmniVision OV5647 cameras.
+ *
+ * Based on Samsung S5K6AAFX SXGA 1/6" 1.3M CMOS Image Sensor driver
+ * Copyright (C) 2011 Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx>
+ *
+ * Based on Omnivision OV7670 Camera Driver
+ * Copyright (C) 2006-7 Jonathan Corbet <corbet@xxxxxxx>
+ *
+ * Copyright (C) 2016, Synopsys, Inc.
+ *
+ * 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 version 2.
+ *
+ * This program is distributed .as is. WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/videodev2.h>
+#include <media/v4l2-device.h>
+#include <media/v4l2-image-sizes.h>
+#include <media/v4l2-mediabus.h>
+#include <media/v4l2-of.h>
+
+#define SENSOR_NAME "ov5647"
+
+#define OV5647_SW_RESET 0x0103
+#define OV5647_REG_CHIPID_H 0x300A
+#define OV5647_REG_CHIPID_L 0x300B
+
+#define REG_TERM 0xfffe
+#define VAL_TERM 0xfe
+#define REG_DLY 0xffff
+
+#define OV5647_ROW_START 0x01
+#define OV5647_ROW_START_MIN 0
+#define OV5647_ROW_START_MAX 2004
+#define OV5647_ROW_START_DEF 54
+
+#define OV5647_COLUMN_START 0x02
+#define OV5647_COLUMN_START_MIN 0
+#define OV5647_COLUMN_START_MAX 2750
+#define OV5647_COLUMN_START_DEF 16
+
+#define OV5647_WINDOW_HEIGHT 0x03
+#define OV5647_WINDOW_HEIGHT_MIN 2
+#define OV5647_WINDOW_HEIGHT_MAX 2006
+#define OV5647_WINDOW_HEIGHT_DEF 1944
+
+#define OV5647_WINDOW_WIDTH 0x04
+#define OV5647_WINDOW_WIDTH_MIN 2
+#define OV5647_WINDOW_WIDTH_MAX 2752
+#define OV5647_WINDOW_WIDTH_DEF 2592
+
+struct regval_list {
+ u16 addr;
+ u8 data;
+};
+
+struct ov5647 {
+ struct v4l2_subdev sd;
+ struct media_pad pad;
+ struct mutex lock;
+ struct v4l2_mbus_framefmt format;
+ unsigned int width;
+ unsigned int height;
+ int power_count;
+ struct clk *xclk;
+};
+
+static inline struct ov5647 *to_state(struct v4l2_subdev *sd)
+{
+ return container_of(sd, struct ov5647, sd);
+}
+
+static struct regval_list sensor_oe_disable_regs[] = {
+ {0x3000, 0x00},
+ {0x3001, 0x00},
+ {0x3002, 0x00},
+};
+
+static struct regval_list sensor_oe_enable_regs[] = {
+ {0x3000, 0x0f},
+ {0x3001, 0xff},
+ {0x3002, 0xe4},
+};
+
+static struct regval_list ov5647_640x480[] = {
+ {0x0100, 0x00},
+ {0x0103, 0x01},
+ {0x3034, 0x08},
+ {0x3035, 0x21},
+ {0x3036, 0x46},
+ {0x303c, 0x11},
+ {0x3106, 0xf5},
+ {0x3821, 0x07},
+ {0x3820, 0x41},
+ {0x3827, 0xec},
+ {0x370c, 0x0f},
+ {0x3612, 0x59},
+ {0x3618, 0x00},
+ {0x5000, 0x06},
+ {0x5001, 0x01},
+ {0x5002, 0x41},
+ {0x5003, 0x08},
+ {0x5a00, 0x08},
+ {0x3000, 0x00},
+ {0x3001, 0x00},
+ {0x3002, 0x00},
+ {0x3016, 0x08},
+ {0x3017, 0xe0},
+ {0x3018, 0x44},
+ {0x301c, 0xf8},
+ {0x301d, 0xf0},
+ {0x3a18, 0x00},
+ {0x3a19, 0xf8},
+ {0x3c01, 0x80},
+ {0x3b07, 0x0c},
+ {0x380c, 0x07},
+ {0x380d, 0x68},
+ {0x380e, 0x03},
+ {0x380f, 0xd8},
+ {0x3814, 0x31},
+ {0x3815, 0x31},
+ {0x3708, 0x64},
+ {0x3709, 0x52},
+ {0x3808, 0x02},
+ {0x3809, 0x80},
+ {0x380a, 0x01},
+ {0x380b, 0xE0},
+ {0x3801, 0x00},
+ {0x3802, 0x00},
+ {0x3803, 0x00},
+ {0x3804, 0x0a},
+ {0x3805, 0x3f},
+ {0x3806, 0x07},
+ {0x3807, 0xa1},
+ {0x3811, 0x08},
+ {0x3813, 0x02},
+ {0x3630, 0x2e},
+ {0x3632, 0xe2},
+ {0x3633, 0x23},
+ {0x3634, 0x44},
+ {0x3636, 0x06},
+ {0x3620, 0x64},
+ {0x3621, 0xe0},
+ {0x3600, 0x37},
+ {0x3704, 0xa0},
+ {0x3703, 0x5a},
+ {0x3715, 0x78},
+ {0x3717, 0x01},
+ {0x3731, 0x02},
+ {0x370b, 0x60},
+ {0x3705, 0x1a},
+ {0x3f05, 0x02},
+ {0x3f06, 0x10},
+ {0x3f01, 0x0a},
+ {0x3a08, 0x01},
+ {0x3a09, 0x27},
+ {0x3a0a, 0x00},
+ {0x3a0b, 0xf6},
+ {0x3a0d, 0x04},
+ {0x3a0e, 0x03},
+ {0x3a0f, 0x58},
+ {0x3a10, 0x50},
+ {0x3a1b, 0x58},
+ {0x3a1e, 0x50},
+ {0x3a11, 0x60},
+ {0x3a1f, 0x28},
+ {0x4001, 0x02},
+ {0x4004, 0x02},
+ {0x4000, 0x09},
+ {0x4837, 0x24},
+ {0x4050, 0x6e},
+ {0x4051, 0x8f},
+ {0x0100, 0x01},
+};
+
+static int ov5647_write(struct v4l2_subdev *sd, u16 reg, u8 val)
+{
+ int ret;
+ unsigned char data[3] = { reg >> 8, reg & 0xff, val};
+ struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+ ret = i2c_master_send(client, data, 3);
+ if (ret < 0)
+ dev_dbg(&client->dev, "%s: i2c write error, reg: %x\n",
+ __func__, reg);
+
+ return ret;
+}
+
+static int ov5647_read(struct v4l2_subdev *sd, u16 reg, u8 *val)
+{
+ int ret;
+ unsigned char data_w[2] = { reg >> 8, reg & 0xff };
+ struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+ ret = i2c_master_send(client, data_w, 2);
+ if (ret < 0) {
+ dev_dbg(&client->dev, "%s: i2c write error, reg: %x\n",
+ __func__, reg);
+ return ret;
+ }
+
+ ret = i2c_master_recv(client, val, 1);
+ if (ret < 0)
+ dev_dbg(&client->dev, "%s: i2c read error, reg: %x\n",
+ __func__, reg);
+
+ return ret;
+}
+
+static int ov5647_write_array(struct v4l2_subdev *sd,
+ struct regval_list *regs, int array_size)
+{
+ int i, ret;
+
+ for (i = 0; i < array_size; i++) {
+ ret = ov5647_write(sd, regs[i].addr, regs[i].data);
+ if (ret < 0)
+ return ret;
+ }
+
+ return 0;
+}
+
+static int ov5647_set_virtual_channel(struct v4l2_subdev *sd, int channel)
+{
+ u8 channel_id;
+ int ret;
+
+ ret = ov5647_read(sd, 0x4814, &channel_id);
+ if (ret < 0)
+ return ret;
+
+ channel_id &= ~(3 << 6);
+ return ov5647_write(sd, 0x4814, channel_id | (channel << 6));
+}
+
+static int ov5647_stream_on(struct v4l2_subdev *sd)
+{
+ int ret;
+
+ ret = ov5647_write(sd, 0x4202, 0x00);
+ if (ret < 0)
+ return ret;
+
+ return ov5647_write(sd, 0x300D, 0x00);
+}
+
+static int ov5647_stream_off(struct v4l2_subdev *sd)
+{
+ int ret;
+
+ ret = ov5647_write(sd, 0x4202, 0x0f);
+ if (ret < 0)
+ return ret;
+
+ return ov5647_write(sd, 0x300D, 0x01);
+}
+
+static int set_sw_standby(struct v4l2_subdev *sd, bool standby)
+{
+ int ret;
+ u8 rdval;
+
+ ret = ov5647_read(sd, 0x0100, &rdval);
+ if (ret < 0)
+ return ret;
+
+ if (standby)
+ rdval &= ~0x01;
+ else
+ rdval |= 0x01;
+
+ return ov5647_write(sd, 0x0100, rdval);
+}
+
+static int __sensor_init(struct v4l2_subdev *sd)
+{
+ int ret;
+ u8 resetval, rdval;
+ struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+ dev_dbg(&client->dev, "sensor init\n");
+
+ ret = ov5647_read(sd, 0x0100, &rdval);
+ if (ret < 0)
+ return ret;
+
+ ret = ov5647_write_array(sd, ov5647_640x480,
+ ARRAY_SIZE(ov5647_640x480));
+ if (ret < 0) {
+ dev_err(&client->dev, "write sensor default regs error\n");
+ return ret;
+ }
+
+ ret = ov5647_set_virtual_channel(sd, 0);
+ if (ret < 0)
+ return ret;
+
+ ret = ov5647_read(sd, 0x0100, &resetval);
+ if (ret < 0)
+ return ret;
+
+ if (!(resetval & 0x01)) {
+ dev_err(&client->dev, "Device was in SW standby");
+ ret = ov5647_write(sd, 0x0100, 0x01);
+ if (ret < 0)
+ return ret;
+ }
+
+ return ov5647_write(sd, 0x4800, 0x04);
+}
+
+static int ov5647_sensor_power(struct v4l2_subdev *sd, int on)
+{
+ int ret = 0;
+ struct ov5647 *ov5647 = to_state(sd);
+ struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+ mutex_lock(&ov5647->lock);
+
+ if (on && !ov5647->power_count) {
+ dev_dbg(&client->dev, "OV5647 power on\n");
+
+ ret = clk_prepare_enable(ov5647->xclk);
+ if (ret < 0) {
+ dev_err(&client->dev, "clk prepare enable failed\n");
+ goto out;
+ }
+
+ ret = ov5647_write_array(sd, sensor_oe_enable_regs,
+ ARRAY_SIZE(sensor_oe_enable_regs));
+ if (ret < 0) {
+ clk_disable_unprepare(ov5647->xclk);
+ dev_err(&client->dev,
+ "write sensor_oe_enable_regs error\n");
+ goto out;
+ }
+
+ ret = __sensor_init(sd);
+ if (ret < 0) {
+ clk_disable_unprepare(ov5647->xclk);
+ dev_err(&client->dev,
+ "Camera not available, check Power\n");
+ goto out;
+ }
+ } else if (!on && ov5647->power_count == 1) {
+ dev_dbg(&client->dev, "OV5647 power off\n");
+
+ ret = ov5647_write_array(sd, sensor_oe_disable_regs,
+ ARRAY_SIZE(sensor_oe_disable_regs));
+
+ if (ret < 0)
+ dev_dbg(&client->dev, "disable oe failed\n");
+
+ ret = set_sw_standby(sd, true);
+
+ if (ret < 0)
+ dev_dbg(&client->dev, "soft stby failed\n");
+
+ clk_disable_unprepare(ov5647->xclk);
+ }
+
+ /* Update the power count. */
+ ov5647->power_count += on ? 1 : -1;
+ WARN_ON(ov5647->power_count < 0);
+
+out:
+ mutex_unlock(&ov5647->lock);
+
+ return ret;
+}
+
+#ifdef CONFIG_VIDEO_ADV_DEBUG
+static int ov5647_sensor_get_register(struct v4l2_subdev *sd,
+ struct v4l2_dbg_register *reg)
+{
+ u8 val;
+ int ret;
+
+ ret = ov5647_read(sd, reg->reg & 0xff, &val);
+ if (ret < 0)
+ return ret;
+
+ reg->val = val;
+ reg->size = 1;
+
+ return 0;
+}
+
+static int ov5647_sensor_set_register(struct v4l2_subdev *sd,
+ const struct v4l2_dbg_register *reg)
+{
+ return ov5647_write(sd, reg->reg & 0xff, reg->val & 0xff);
+}
+#endif
+
+/**
+ * @short Subdev core operations registration
+ */
+static const struct v4l2_subdev_core_ops ov5647_subdev_core_ops = {
+ .s_power = ov5647_sensor_power,
+#ifdef CONFIG_VIDEO_ADV_DEBUG
+ .g_register = ov5647_sensor_get_register,
+ .s_register = ov5647_sensor_set_register,
+#endif
+};
+
+static int ov5647_s_stream(struct v4l2_subdev *sd, int enable)
+{
+ if (enable)
+ return ov5647_stream_on(sd);
+ else
+ return ov5647_stream_off(sd);
+}
+
+static const struct v4l2_subdev_video_ops ov5647_subdev_video_ops = {
+ .s_stream = ov5647_s_stream,
+};
+
+static int ov5647_enum_mbus_code(struct v4l2_subdev *sd,
+ struct v4l2_subdev_pad_config *cfg,
+ struct v4l2_subdev_mbus_code_enum *code)
+{
+ if (code->index > 0)
+ return -EINVAL;
+
+ code->code = MEDIA_BUS_FMT_SBGGR8_1X8;
+
+ return 0;
+}
+
+static const struct v4l2_subdev_pad_ops ov5647_subdev_pad_ops = {
+ .enum_mbus_code = ov5647_enum_mbus_code,
+};
+
+static const struct v4l2_subdev_ops ov5647_subdev_ops = {
+ .core = &ov5647_subdev_core_ops,
+ .video = &ov5647_subdev_video_ops,
+ .pad = &ov5647_subdev_pad_ops,
+};
+
+static int ov5647_detect(struct v4l2_subdev *sd)
+{
+ u8 read;
+ int ret;
+ struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+ ret = ov5647_write(sd, OV5647_SW_RESET, 0x01);
+ if (ret < 0)
+ return ret;
+
+ ret = ov5647_read(sd, OV5647_REG_CHIPID_H, &read);
+ if (ret < 0)
+ return ret;
+
+ if (read != 0x56) {
+ dev_err(&client->dev, "ID High expected 0x56 got %x", read);
+ return -ENODEV;
+ }
+
+ ret = ov5647_read(sd, OV5647_REG_CHIPID_L, &read);
+ if (ret < 0)
+ return ret;
+
+ if (read != 0x47) {
+ dev_err(&client->dev, "ID Low expected 0x47 got %x", read);
+ return -ENODEV;
+ }
+
+ return ov5647_write(sd, OV5647_SW_RESET, 0x00);
+}
+
+static int ov5647_open(struct v4l2_subdev *sd, struct v4l2_subdev_fh *fh)
+{
+ struct v4l2_mbus_framefmt *format =
+ v4l2_subdev_get_try_format(sd, fh->pad, 0);
+ struct v4l2_rect *crop =
+ v4l2_subdev_get_try_crop(sd, fh->pad, 0);
+
+ crop->left = OV5647_COLUMN_START_DEF;
+ crop->top = OV5647_ROW_START_DEF;
+ crop->width = OV5647_WINDOW_WIDTH_DEF;
+ crop->height = OV5647_WINDOW_HEIGHT_DEF;
+
+ format->code = MEDIA_BUS_FMT_SBGGR8_1X8;
+
+ format->width = OV5647_WINDOW_WIDTH_DEF;
+ format->height = OV5647_WINDOW_HEIGHT_DEF;
+ format->field = V4L2_FIELD_NONE;
+ format->colorspace = V4L2_COLORSPACE_SRGB;
+
+ return 0;
+}
+
+static const struct v4l2_subdev_internal_ops ov5647_subdev_internal_ops = {
+ .open = ov5647_open,
+};
+
+static int ov5647_parse_dt(struct device_node *np)
+{
+ struct v4l2_of_endpoint bus_cfg;
+ struct device_node *ep;
+
+ int ret;
+
+ ep = of_graph_get_next_endpoint(np, NULL);
+ if (!ep)
+ return -EINVAL;
+
+ ret = v4l2_of_parse_endpoint(ep, &bus_cfg);
+
+ of_node_put(ep);
+ return ret;
+}
+
+static int ov5647_probe(struct i2c_client *client,
+ const struct i2c_device_id *id)
+{
+ struct device *dev = &client->dev;
+ struct ov5647 *sensor;
+ int ret;
+ struct v4l2_subdev *sd;
+ struct device_node *np = client->dev.of_node;
+ u32 xclk_freq;
+
+ sensor = devm_kzalloc(dev, sizeof(*sensor), GFP_KERNEL);
+ if (!sensor)
+ return -ENOMEM;
+
+ if (IS_ENABLED(CONFIG_OF) && np) {
+ ret = ov5647_parse_dt(np);
+ if (ret) {
+ dev_err(dev, "DT parsing error: %d\n", ret);
+ return ret;
+ }
+ }
+
+ /* get system clock (xclk) */
+ sensor->xclk = devm_clk_get(dev, NULL);
+ if (IS_ERR(sensor->xclk)) {
+ dev_err(dev, "could not get xclk");
+ return PTR_ERR(sensor->xclk);
+ }
+
+ xclk_freq = clk_get_rate(sensor->xclk);
+ if (xclk_freq != 25000000) {
+ dev_err(dev, "Unsupported clock frequency: %u\n", xclk_freq);
+ return -EINVAL;
+ }
+
+ mutex_init(&sensor->lock);
+
+ sd = &sensor->sd;
+ v4l2_i2c_subdev_init(sd, client, &ov5647_subdev_ops);
+ sensor->sd.internal_ops = &ov5647_subdev_internal_ops;
+ sensor->sd.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
+
+ sensor->pad.flags = MEDIA_PAD_FL_SOURCE;
+ sd->entity.function = MEDIA_ENT_F_CAM_SENSOR;
+ ret = media_entity_pads_init(&sd->entity, 1, &sensor->pad);
+ if (ret < 0)
+ goto mutex_remove;
+
+ ret = ov5647_detect(sd);
+ if (ret < 0)
+ goto error;
+
+ ret = v4l2_async_register_subdev(sd);
+ if (ret < 0)
+ goto error;
+
+ dev_dbg(dev, "OmniVision OV5647 camera driver probed\n");
+ return 0;
+error:
+ media_entity_cleanup(&sd->entity);
+mutex_remove:
+ mutex_destroy(&sensor->lock);
+ return ret;
+}
+
+static int ov5647_remove(struct i2c_client *client)
+{
+ struct v4l2_subdev *sd = i2c_get_clientdata(client);
+ struct ov5647 *ov5647 = to_state(sd);
+
+ v4l2_async_unregister_subdev(&ov5647->sd);
+ media_entity_cleanup(&ov5647->sd.entity);
+ v4l2_device_unregister_subdev(sd);
+ mutex_destroy(&ov5647->lock);
+
+ return 0;
+}
+
+static const struct i2c_device_id ov5647_id[] = {
+ { "ov5647", 0 },
+ { }
+};
+MODULE_DEVICE_TABLE(i2c, ov5647_id);
+
+#if IS_ENABLED(CONFIG_OF)
+static const struct of_device_id ov5647_of_match[] = {
+ { .compatible = "ovti,ov5647" },
+ { /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, ov5647_of_match);
+#endif
+
+static struct i2c_driver ov5647_driver = {
+ .driver = {
+ .of_match_table = of_match_ptr(ov5647_of_match),
+ .name = SENSOR_NAME,
+ },
+ .probe = ov5647_probe,
+ .remove = ov5647_remove,
+ .id_table = ov5647_id,
+};
+
+module_i2c_driver(ov5647_driver);
+
+MODULE_AUTHOR("Ramiro Oliveira <roliveir@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("A low-level driver for OmniVision ov5647 sensors");
+MODULE_LICENSE("GPL v2");
--
2.11.0
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
