[PATCH v4 7/7] platform/chrome: Expose Chrome OS Lightbar to users

Javier Martinez Canillas
2015-01-29T13:38:40Z

From: Bill Richardson <wfrichar@chromium.org>

This adds some sysfs entries to provide userspace control of the
four-element LED "lightbar" on the Chromebook Pixel. This only instantiates
the lightbar controls if the device actually exists.

To prevent DoS attacks, this interface is limited to 20 accesses/second,
although that rate can be adjusted by a privileged user.

On Chromebooks without a lightbar, this should have no effect. On the
Chromebook Pixel, you should be able to do things like this:

$ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
$ echo 0x80 > brightness
$ echo 255 > brightness
$
$ cat sequence
S0
$ echo konami > sequence
$ cat sequence
KONAMI
$
$ cat sequence
S0

And

$ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
$ echo stop > sequence
$ echo "4 255 255 255" > led_rgb
$ echo "0 255 0 0 1 0 255 0 2 0 0 255 3 255 255 0" > led_rgb
$ echo run > sequence

Test the DoS prevention with this:

$ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
$ echo 500 > interval_msec
$ time (cat version version version version version version version)

Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
---

Changes since v3: None.

Changes since v2: None.

Changes since v1:
- Moved from drivers/mfd to drivers/platform/chrome.
- Modify to use the fixed-size arrays for cros_ec_command in and out buffers.
---
drivers/platform/chrome/Makefile | 2 +-
drivers/platform/chrome/cros_ec_dev.c | 2 +
drivers/platform/chrome/cros_ec_dev.h | 3 +
drivers/platform/chrome/cros_ec_lightbar.c | 367 +++++++++++++++++++++++++++++
4 files changed, 373 insertions(+), 1 deletion(-)
create mode 100644 drivers/platform/chrome/cros_ec_lightbar.c

diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
index 3e7980b9bc86..cc5d2f294c40 100644
--- a/drivers/platform/chrome/Makefile
+++ b/drivers/platform/chrome/Makefile
@@ -1,5 +1,5 @@

obj-$(CONFIG_CHROMEOS_LAPTOP) += chromeos_laptop.o
obj-$(CONFIG_CHROMEOS_PSTORE) += chromeos_pstore.o
-cros_ec_devs-objs := cros_ec_dev.o cros_ec_sysfs.o
+cros_ec_devs-objs := cros_ec_dev.o cros_ec_sysfs.o cros_ec_lightbar.o
obj-$(CONFIG_CROS_EC_CHARDEV) += cros_ec_devs.o
diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
index 33f37ad36892..ce714317a59e 100644
--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -200,6 +200,7 @@ static int ec_device_probe(struct platform_device *pdev)

/* Initialize extra interfaces */
ec_dev_sysfs_init(ec);
+ ec_dev_lightbar_init(ec);

return 0;
}
@@ -208,6 +209,7 @@ static int ec_device_remove(struct platform_device *pdev)
{
struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);

+ ec_dev_lightbar_remove(ec);
ec_dev_sysfs_remove(ec);
device_destroy(cros_class, MKDEV(ec_major, 0));
cdev_del(&ec->cdev);
diff --git a/drivers/platform/chrome/cros_ec_dev.h b/drivers/platform/chrome/cros_ec_dev.h
index f03613290ecf..45d67f7e518c 100644
--- a/drivers/platform/chrome/cros_ec_dev.h
+++ b/drivers/platform/chrome/cros_ec_dev.h
@@ -47,4 +47,7 @@ struct cros_ec_readmem {
void ec_dev_sysfs_init(struct cros_ec_device *);
void ec_dev_sysfs_remove(struct cros_ec_device *);

+void ec_dev_lightbar_init(struct cros_ec_device *);
+void ec_dev_lightbar_remove(struct cros_ec_device *);
+
#endif /* _CROS_EC_DEV_H_ */
diff --git a/drivers/platform/chrome/cros_ec_lightbar.c b/drivers/platform/chrome/cros_ec_lightbar.c
new file mode 100644
index 000000000000..35fc892e4c95
--- /dev/null
+++ b/drivers/platform/chrome/cros_ec_lightbar.c
@@ -0,0 +1,367 @@
+/*
+ * cros_ec_lightbar - expose the Chromebook Pixel lightbar to userspace
+ *
+ * Copyright (C) 2014 Google, 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) "cros_ec_lightbar: " fmt
+
+#include <linux/ctype.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/kobject.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/mfd/cros_ec_commands.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+
+#include "cros_ec_dev.h"
+
+/* Rate-limit the lightbar interface to prevent DoS. */
+static unsigned long lb_interval_jiffies = 50 * HZ / 1000;
+
+static ssize_t interval_msec_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ unsigned long msec = lb_interval_jiffies * 1000 / HZ;
+
+ return scnprintf(buf, PAGE_SIZE, "%lu\n", msec);
+}
+
+static ssize_t interval_msec_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned long msec;
+
+ if (kstrtoul(buf, 0, &msec))
+ return -EINVAL;
+
+ lb_interval_jiffies = msec * HZ / 1000;
+
+ return count;
+}
+
+static DEFINE_MUTEX(lb_mutex);
+/* Return 0 if able to throttle correctly, error otherwise */
+static int lb_throttle(void)
+{
+ static unsigned long last_access;
+ unsigned long now, next_timeslot;
+ long delay;
+ int ret = 0;
+
+ mutex_lock(&lb_mutex);
+
+ now = jiffies;
+ next_timeslot = last_access + lb_interval_jiffies;
+
+ if (time_before(now, next_timeslot)) {
+ delay = (long)(next_timeslot) - (long)now;
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (schedule_timeout(delay) > 0) {
+ /* interrupted - just abort */
+ ret = -EINTR;
+ goto out;
+ }
+ now = jiffies;
+ }
+
+ last_access = now;
+out:
+ mutex_unlock(&lb_mutex);
+
+ return ret;
+}
+
+#define INIT_MSG(P, R) { \
+ .command = EC_CMD_LIGHTBAR_CMD, \
+ .outsize = sizeof(*P), \
+ .insize = sizeof(*R), \
+ }
+
+static int get_lightbar_version(struct cros_ec_device *ec,
+ uint32_t *ver_ptr, uint32_t *flg_ptr)
+{
+ struct ec_params_lightbar *param;
+ struct ec_response_lightbar *resp;
+ struct cros_ec_command msg = INIT_MSG(param, resp);
+ int ret;
+
+ param = (struct ec_params_lightbar *)msg.outdata;
+ param->cmd = LIGHTBAR_CMD_VERSION;
+ ret = cros_ec_cmd_xfer(ec, &msg);
+ if (ret < 0)
+ return 0;
+
+ switch (msg.result) {
+ case EC_RES_INVALID_PARAM:
+ /* Pixel had no version command. */
+ if (ver_ptr)
+ *ver_ptr = 0;
+ if (flg_ptr)
+ *flg_ptr = 0;
+ return 1;
+
+ case EC_RES_SUCCESS:
+ resp = (struct ec_response_lightbar *)msg.indata;
+
+ /* Future devices w/lightbars should implement this command */
+ if (ver_ptr)
+ *ver_ptr = resp->version.num;
+ if (flg_ptr)
+ *flg_ptr = resp->version.flags;
+ return 1;
+ }
+
+ /* Anything else (ie, EC_RES_INVALID_COMMAND) - no lightbar */
+ return 0;
+}
+
+static ssize_t version_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ uint32_t version, flags;
+ struct cros_ec_device *ec = dev_get_drvdata(dev);
+ int ret;
+
+ ret = lb_throttle();
+ if (ret)
+ return ret;
+
+ /* This should always succeed, because we check during init. */
+ if (!get_lightbar_version(ec, &version, &flags))
+ return -EIO;
+
+ return scnprintf(buf, PAGE_SIZE, "%d %d\n", version, flags);
+}
+
+static ssize_t brightness_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct ec_params_lightbar *param;
+ struct ec_response_lightbar *resp;
+ struct cros_ec_command msg = INIT_MSG(param, resp);
+ int ret;
+ unsigned int val;
+ struct cros_ec_device *ec = dev_get_drvdata(dev);
+
+ if (kstrtouint(buf, 0, &val))
+ return -EINVAL;
+
+ param = (struct ec_params_lightbar *)msg.outdata;
+ param->cmd = LIGHTBAR_CMD_BRIGHTNESS;
+ param->brightness.num = val;
+ ret = lb_throttle();
+ if (ret)
+ return ret;
+
+ ret = cros_ec_cmd_xfer(ec, &msg);
+ if (ret < 0)
+ return ret;
+
+ if (msg.result != EC_RES_SUCCESS)
+ return -EINVAL;
+
+ return count;
+}
+
+
+/*
+ * We expect numbers, and we'll keep reading until we find them, skipping over
+ * any whitespace (sysfs guarantees that the input is null-terminated). Every
+ * four numbers are sent to the lightbar as <LED,R,G,B>. We fail at the first
+ * parsing error, if we don't parse any numbers, or if we have numbers left
+ * over.
+ */
+static ssize_t led_rgb_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct ec_params_lightbar *param;
+ struct ec_response_lightbar *resp;
+ struct cros_ec_command msg = INIT_MSG(param, resp);
+ struct cros_ec_device *ec = dev_get_drvdata(dev);
+ unsigned int val[4];
+ int ret, i = 0, j = 0, ok = 0;
+
+ do {
+ /* Skip any whitespace */
+ while (*buf && isspace(*buf))
+ buf++;
+
+ if (!*buf)
+ break;
+
+ ret = sscanf(buf, "%i", &val[i++]);
+ if (ret == 0)
+ return -EINVAL;
+
+ if (i == 4) {
+ param = (struct ec_params_lightbar *)msg.outdata;
+ param->cmd = LIGHTBAR_CMD_RGB;
+ param->rgb.led = val[0];
+ param->rgb.red = val[1];
+ param->rgb.green = val[2];
+ param->rgb.blue = val[3];
+ /*
+ * Throttle only the first of every four transactions,
+ * so that the user can update all four LEDs at once.
+ */
+ if ((j++ % 4) == 0) {
+ ret = lb_throttle();
+ if (ret)
+ return ret;
+ }
+
+ ret = cros_ec_cmd_xfer(ec, &msg);
+ if (ret < 0)
+ return ret;
+
+ if (msg.result != EC_RES_SUCCESS)
+ return -EINVAL;
+
+ i = 0;
+ ok = 1;
+ }
+
+ /* Skip over the number we just read */
+ while (*buf && !isspace(*buf))
+ buf++;
+
+ } while (*buf);
+
+ return (ok && i == 0) ? count : -EINVAL;
+}
+
+static const char const *seqname[] = {
+ "ERROR", "S5", "S3", "S0", "S5S3", "S3S0",
+ "S0S3", "S3S5", "STOP", "RUN", "PULSE", "TEST", "KONAMI",
+};
+
+static ssize_t sequence_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct ec_params_lightbar *param;
+ struct ec_response_lightbar *resp;
+ struct cros_ec_command msg = INIT_MSG(param, resp);
+ int ret;
+ struct cros_ec_device *ec = dev_get_drvdata(dev);
+
+ param = (struct ec_params_lightbar *)msg.outdata;
+ param->cmd = LIGHTBAR_CMD_GET_SEQ;
+ ret = lb_throttle();
+ if (ret)
+ return ret;
+
+ ret = cros_ec_cmd_xfer(ec, &msg);
+ if (ret < 0)
+ return ret;
+
+ if (msg.result != EC_RES_SUCCESS)
+ return scnprintf(buf, PAGE_SIZE,
+ "ERROR: EC returned %d\n", msg.result);
+
+ resp = (struct ec_response_lightbar *)msg.indata;
+ if (resp->get_seq.num >= ARRAY_SIZE(seqname))
+ return scnprintf(buf, PAGE_SIZE, "%d\n", resp->get_seq.num);
+ else
+ return scnprintf(buf, PAGE_SIZE, "%s\n",
+ seqname[resp->get_seq.num]);
+}
+
+static ssize_t sequence_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct ec_params_lightbar *param;
+ struct ec_response_lightbar *resp;
+ struct cros_ec_command msg = INIT_MSG(param, resp);
+ unsigned int num;
+ int ret, len;
+ struct cros_ec_device *ec = dev_get_drvdata(dev);
+
+ for (len = 0; len < count; len++)
+ if (!isalnum(buf[len]))
+ break;
+
+ for (num = 0; num < ARRAY_SIZE(seqname); num++)
+ if (!strncasecmp(seqname[num], buf, len))
+ break;
+
+ if (num >= ARRAY_SIZE(seqname)) {
+ ret = kstrtouint(buf, 0, &num);
+ if (ret)
+ return ret;
+ }
+
+ param = (struct ec_params_lightbar *)msg.outdata;
+ param->cmd = LIGHTBAR_CMD_SEQ;
+ param->seq.num = num;
+ ret = lb_throttle();
+ if (ret)
+ return ret;
+
+ ret = cros_ec_cmd_xfer(ec, &msg);
+ if (ret < 0)
+ return ret;
+
+ if (msg.result != EC_RES_SUCCESS)
+ return -EINVAL;
+
+ return count;
+}
+
+/* Module initialization */
+
+static DEVICE_ATTR_RW(interval_msec);
+static DEVICE_ATTR_RO(version);
+static DEVICE_ATTR_WO(brightness);
+static DEVICE_ATTR_WO(led_rgb);
+static DEVICE_ATTR_RW(sequence);
+static struct attribute *__lb_cmds_attrs[] = {
+ &dev_attr_interval_msec.attr,
+ &dev_attr_version.attr,
+ &dev_attr_brightness.attr,
+ &dev_attr_led_rgb.attr,
+ &dev_attr_sequence.attr,
+ NULL,
+};
+static struct attribute_group lb_cmds_attr_group = {
+ .name = "lightbar",
+ .attrs = __lb_cmds_attrs,
+};
+
+void ec_dev_lightbar_init(struct cros_ec_device *ec)
+{
+ int ret = 0;
+
+ /* Only instantiate this stuff if the EC has a lightbar */
+ if (!get_lightbar_version(ec, NULL, NULL))
+ return;
+
+ ret = sysfs_create_group(&ec->vdev->kobj, &lb_cmds_attr_group);
+ if (ret)
+ pr_warn("sysfs_create_group() failed: %d\n", ret);
+}
+
+void ec_dev_lightbar_remove(struct cros_ec_device *ec)
+{
+ sysfs_remove_group(&ec->vdev->kobj, &lb_cmds_attr_group);
+}
--
2.1.3